Cruise Control: Description and Operation
66 03 04 (086)
Cruise control
E90, E91, E92, E93
Introduction
The following cruise controls are available at the start of series production of the E90 (12/2004):
- Option 540 "Cruise control"
The set speed is maintained via the engine. (Set speed = stored desired speed)
- Accelerating to the set speed: Engine intervention via the DME/DDE
(DME = "digital engine electronics"; DDE = "digital diesel electronics")
- Decelerating to the set speed: Via the engine drag-torque
- Option 541 "Active Cruise Control"
With Active Cruise Control, a timed separation is maintained from the vehicle ahead. The separation can be adjusted.
- Accelerating to the set speed: Engine intervention via the DME/DDE
- Decelerating to the set speed: Brake intervention via the DSC (Dynamic Stability Control)
- Option 544 "Cruise control with brake function"
The set speed is maintained via engine and brake intervention.
- Accelerating to the set speed: Engine intervention via the DME/DDE
- Decelerating to the set speed: Brake intervention via the DSC
Important: Cruise control does not relieve the driver of his personal responsibility.
Cruise control is a comfort system. Adjustments by the driver will always have a higher priority (= importance) than cruise control.
The driver should decide whether (and how) the system is used based on road and traffic conditions and visibility.
With the start of series production of the E90, longitudinal dynamics management (LDM) will also be introduced.
Longitudinal dynamics management consists of various function blocks (e.g.: Cruise control with brake function or Active Cruise Control option). These function blocks are grouped together into a control unit by the corresponding software. The control unit is called the LDM control unit.
The LDM control unit evaluates all relevant data for cruise control. (e.g.: The ACC sensor sends the information "Vehicle monitored". This information is evaluated in the LDM control unit).
> - E92 from 06/2006 and
E90, E91 from 09/2006 and
E93 from 12/2006
The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit.
In this SI Technology (SBT) bulletin, only longitudinal dynamic management and thus the Cruise control with brake function or Active Cruise Control option is described.
Longitudinal dynamics management is available in connection with the following option (special equipment):
- Option 541 "Active Cruise Control"
or
- Option 544 "Cruise control with brake function"
> - E92 from 06/2006 and
E90, E91 from 09/2006 and
E93 from 12/2006
The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit.
Option 541 "Active Cruise Control"
The 2nd generation Active Cruise Control option will be used for the first time with the E63/E64 from 09/2004.
Active Cruise Control is a comfortable spacing and cruise control.
The distance from the vehicle ahead can be selected from 4 fixed timed separations. (EURO version: 1.0 - 1.5 - 2.0 - 2.5 seconds)
This means that the as speed changes, so does the distance to the vehicle ahead.
The legally prescribed minimum distance is not undershot when control is active.
Differences between option "Active Cruise Control" on E90, E91, E92, E93 and option "Active Cruise Control" on E60, E61, E63, E64, E65, E66:
- On the E90, E91, E92 (including all-wheel drive) and E93, the data for the longitudinal dynamic management are evaluated in the LDM control unit.
- On the E60, E61, E63, E64, E65, E66, the data for the longitudinal dynamic management are evaluated in the ACC control unit (i.e.: there is no LDM control unit fitted).
[for further information, please refer to SI Technology (SBT) 66 01 04 067]
Option 544 "Cruise control with brake function"
Differences between "cruise control with brake function" and "cruise control":
- Constant roadspeed, even downhill:
The set speed is also maintained when going downhill. (Brake intervention via the DSC)
- The lateral acceleration in bends is restricted to a comfortable level.
- Indicator disc in the instrument cluster:
The indicator disc shows the set speed.
- Brief display in the LCD display of the instrument cluster:
The newly selected set speed is shown briefly in the LCD display.
Brief description of components
The following components send signals for the cruise control:
- Cruise-control system steering-column stalk
Cruise control is set and called up using the cruise control system steering-column stalk.
- ACC sensor
The ACC sensor monitors the distance, angle and relative speed of vehicles driving ahead. (Relative speed: The relative speed is the speed difference between the two moving objects, that is, the speed difference of the two objects relative to each other.)
The ACC sensor is a radar sensor. The ACC sensor has a limited monitoring range (approx. 120 metres).
- LDM control unit
The LDM control unit is the interface to the engine and to the brakes.
In the LDM control unit, the driver's entries regarding the cruise control system are monitored and evaluated.
The "cruise control with brake function" option is integrated in the LDM control unit.
> - E92 from 06/2006 and
E90, E91 from 09/2006 and
E93 from 12/2006
The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit.
If Active Cruise Control is fitted, the LDM control unit evaluates the data sent from the ACC sensor.
The LDM also communicates with the following control units:
- Instrument cluster
The instrument cluster shows all displays for cruise control.
- An indicator disc in the round instrument shows the set speed.
- The LCD display briefly shows the newly selected set speed (approximately 6 seconds).
- In addition, the LCD display also shows a Check-Control message.
With Active Cruise Control, there are also the following displays:
- Monitored vehicle
(Display through lit icon in the instrument cluster)
- Request for action to driver
(Display through flashing icon in the instrument cluster. Depending on the national version, an acoustic warning is also made.)
- Selected distance from vehicle driving ahead
(Display via icon in the instrument cluster)
- DSC: Dynamic Stability Control
The current status of the vehicle is detected by the DSC, e.g. by evaluating the following sensor signals:
- Rate of yaw (measure of movement of the car about its vertical axis)
- Steering angle
- Information on the brake pressure
- Circumferential wheel speed
The DSC then transmits data about the current vehicle status to the LDM.
The following data is transmitted by the LDM to the DSC:
- Request for vehicle deceleration
The request for vehicle deceleration from the LDM is received by the DSC via the PT-CAN. DSC reduces the speed. To do this, DSC intervenes in the brake system. (goal: comfortable vehicle deceleration. No DSC intervention in the sense of enhanced operating stability.)
> - E92 from 06/2006 and
E90, E91 from 09/2006 and
E93 from 12/2006
The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit.
With automatic braking, the brake lights are activated depending on vehicle deceleration (legally prescribed).
- DME or DDE: Digital engine electronics or digital diesel electronics
The DME/DDE controls the engine intervention. The following data is transmitted by the LDM to the DME or DDE:
- Current torque request
The following data is transmitted to the LDM from the DME or the DDE:
- Driver's command (signals from accelerator pedal module)
> - E92 from 06/2006 and
E90, E91 from 09/2006 and
E93 from 12/2006
The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit.
- JBE: Junction box electronics
The JBE is the data interface (= gateway) between the K-CAN and the PT-CAN.
(K-CAN = body CAN; PT-CAN = powertrain CAN.)
Signals from the F-CAN (Chassis CAN) are simply looped through. (No signal processing in the JBE. The F-CAN cables are simply routed through the junction box housing.)
The junction box consists of the junction box electronics and the electrical distribution centre.
The diagnosis cable is connected to the junction-box electronics.
- FPM: Accelerator pedal module
The accelerator pedal module signals the driver's command. This signal is required to check the respective driving status. (evaluation via DME/DDE)
By pressing the accelerator pedal, the specified speed of the cruise control can be overridden at any time.
- Brake light switch
The brake light switch tells the cruise control system when the brake pedal has been pressed. Cruise control is deactivated if braking actions are necessary.
- Clutch mode (manual transmission only)
Clutch engagement/disengagement is recognised by the signal from the clutch module.
During the clutch engagement/disengagement process, the engine speed is maintained at an optimal speed range by the DME or DDE.
After the clutch has been reengaged, the DME/DDE will adjust back to the current torque request from the Active Cruise Control.
If the engine speed is too high or too low, an audible signal and a Check-Control message prompt the driver to change gear. The prompt to upshift when the engine speed is too high is only made during the warm-up phase of the engine.
Important: Only install prescribed rear differential unit.
Active Cruise Control has a variant encoding which is co-ordinated with the differential ratio. If a different rear differential unit is installed, it may be the case that Active Cruise Control will deactivate itself in manual transmissions, particularly in the higher gears. In this case, no fault is entered in the fault memory.
- EGS: Electronic transmission control
The evaluated cruise control data is sent from the LDM control unit to the DME or DDE. The EGS evaluates the data from the DME or DDE.
The adaptive transmission control (constituent component of electronic transmission control) adapts the shift characteristics of the driving programme to the driver's commands and the driving situation.
- SZL: Steering column switch cluster
The SZL processes all data from the cruise-control system steering-column stalk.
The evaluated switch signals are sent by the SZL through the F-CAN to the LDM control unit.
Signal path:
Cruise control system steering-column stalk -> SZL -> F-CAN -> DSC control unit (acts as a gateway) -> PT-CAN -> LDM control unit
> - E92 from 06/2006 and
E90, E91 from 09/2006 and
E93 from 12/2006
The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit.
- FRM: Footwell module
When cruise control is in operation, the brake lights are actuated during automatic braking (legal requirement). To this end, a signal must be sent from the DSC to the footwell module via the PT-CAN.
The option "Active Cruise Control" uses the "turn signals" signal from the footwell module for assistance when changing lanes. In other words, if a left turn signal is given before overtaking, the distance to the vehicle in front is reduced. The vehicle to be overtaken is "ignored" more easily. Conversely, in the event of a change to the right-hand lane, a vehicle driving there is registered more quickly.
With the vehicle's own calculated expected lane, the sideways deviation of each monitored object can be determined for the vehicle's own lane.
[for further information, please refer to SI Technology (SBT) 61 04 04 094]
- CAS: Car access system
The CAS provides input signals relating to terminal status (e.g. terminal 15 ON).
[for further information, please refer to SI Technology (SBT) 61 03 03 019] Car Access System
- M-ASK or CCC and CID: Multi-audio system controller/Car Communication Computer and Central Information Display
For the instrument cluster, the M-ASK or CCC serves as the interface to the CID. Amongst other things, the CID displays detailed information about the Check-Control messages. To back up the Check-Control message, the M-ASK /CCC emit audible warnings through the loudspeakers (depending on national version). The instrument cluster controls these warnings by means of the K-CAN.
System functions
The system functions of "cruise control with brake function" and "Active Cruise Control" are described below.
Option "Cruise control with brake function"
- Cruise control
Cruise control has the following subfunctions:
- Cruise control system
- Limited lateral acceleration when cornering (up to max. 4.0 m/s2)
Depending on the driving situation, the LDM control unit reports to the DME or DDE or the DSC as follows:
- DME or DDE: Accelerate
- DSC: Brake
> - E92 from 06/2006 and
E90, E91 from 09/2006 and
E93 from 12/2006
The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit.
Option "Active Cruise Control"
- 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
- System limits
Monitor object ahead
Objects are all vehicles in the same lane. The vehicles on other lanes are of no interest for Active Cruise Control.
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
Active Cruise Control 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 Active Cruise Control 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 required for switch-on
-
-
- 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. Active Cruise Control 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, Active Cruise Control 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, Active Cruise Control will be deactivated and a fault will be stored in the fault memory. A Check-Control message will be issued.
System limits
If the limit of the functional range is reached, the driver is prompted to act (brake or swerve) as follows: Display for the monitored vehicle flashes red and an acoustic signal sounds.
During operation, the following system functions, which require explanation, can occur due to the limits of the functional range (for the driver):
- Limited range and deceleration
- The range of the ACC sensor is limited (approximately 120 metres).
Rain, snow and fog absorb radar waves.
This will significantly reduce the range of the ACC sensor.
- Active Cruise Control is only able to effect limited deceleration via the DSC (a maximum of 2.5 m/s2)
This means that cruise control is only able to compensate for a limited relative speed.
Active Cruise Control operation 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 Active Cruise Control.
- 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/s2 to maintain driving comfort.
- Timed separation less than 1 second
The timed separation from a vehicle driving ahead is no less than 1 second when cruise control is active. 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, Active Cruise Control 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
Active 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 system steering-column stalk.
Operation
The range of adjustments for the different cruise control systems are described in the Owner's Handbook.
Notes for service staff
Service staff should note the following points:
- General note:
- Diagnosis: ---
- Encoding/programming: ---
National versions
US and CDN national versions
Different timed separations encoded for following mode (1.5 - 1.8 - 2.2 - 2.5 seconds)
US and GB national versions
The option "Active Cruise Control" is effective in the speed range 20 mph to 110 mph.
Speed can be selected in steps of 1 mph and 5 mph.
Subject to change.