ECO Start/Stop Function Energy Management, Function - GF54.10-P-1040FR

Model 257, 290 up to model year 2021

Function requirements, general

Engine running and at operating temperature
System diagnosis completed without errors
Outside temperature -10 up to 40°C
On-board electrical system battery temperature (G1) 0 up to 60°C
On-board electrical system battery charged sufficiently

Energy management for ECO start/stop function in general

Switching of the engine when the vehicle is at a standstill reduces the fuel consumption and therefore the carbon dioxide emissions. The master control unit for the ECO start/stop function is the powertrain control unit (N127), that records and evaluates all influencing factors. For a stationary vehicle, the ECO start/stop function switches the engine off automatically and starts it again, as soon as the driver wishes to drive off.

It is still possible to stop and start the engine in the conventional way.

Model 290, model 257 except left-hand drive vehicle with engine 264 and code B01 (48V technology) or code U98 (LITHIUM ION STARTER BATTERY (LISB)) or code 228 (Stationary heater) or code 597 (Windshield, heated) or code 811 (Advanced Sound System)

To reduce the drop in voltage perceived by vehicle occupants when starting the engine (e.g. during radio or fan operation), a voltage dip limiter (R62) is installed at the positive terminal of the on-board electrical system battery. The voltage dip limiter is a series resistor that can be switched on and off electronically.

Model 257 (left-hand drive vehicle) with engine 264 except code B01 (48V technology) and except code U98 (LITHIUM ION STARTER BATTERY (LISB)) and except code 228 (Stationary heater) and except code 597 (Windshield, heated) and except code 811 (Advanced Sound System):

To reduce the drop in voltage perceived by vehicle occupants when starting the engine (e.g. during radio or fan operation), a front-end relay (K92) is installed at the positive terminal of the on-board electrical system battery. The front-end relay switches an internal series resistor.

The voltage dip limiter or the front-end relay reduces the power consumption of the starter (M1) when the engine is started and it is connected through circuit 87 to the circuit 50 starter relay (K40/8kH). When starting the engine the voltage dip limiter or the front-end relay has voltage applied to it, the starting procedure is recognized and the series resistor is then activated. If the on-board electrical system voltage dips too far because of the starter's high power consumption, the voltage dip limiter or the front-end relay deactivates the series resistor again.

On vehicles with code B01 (48V technology) the energy required for the starting procedure is provided by the 48 V on-board electrical system. In this instance, a voltage drop is not noticed when starting. The ECO start/stop function encompasses the following subfunctions:

Engine stop
Engine start
Forced engine start

Additional function requirement for engine stop

Stop enable issued by powertrain control unit

Engine stop

As the master control unit for the ECO start/stop function, the powertrain control unit checks various influencing factors for the stop enable. The energy management system provides information for this which describes the on-board electrical system status or the requirements for the on-board electrical system.

The front SAM control unit (N10/6) reads in the data of the battery sensor (B95) (except code U98 (LITHIUM-ION STARTER BATTERY (LISB))) or the data of the control electronics in the on-board electrical system battery (with code U98 (LITHIUM-ION STARTER BATTERY (LISB))) over the battery sensor LIN (LIN B15), evaluates the data and sends information about the condition or the load requests to the 12-V+ on-board electrical system, over the interior CAN (CAN B), electronic | ignition lock control unit (N73) and the chassis FlexRay (Flex E) to the powertrain control unit.

On vehicles with code B01 (48V technology), additional information on the condition of the 48 V on-board electrical system battery (G1/3) is sent by the DC/DC converter control unit (N83/1) over the interior CAN, electronic ignition lock control unit and the suspension FlexRay to the drivetrain control unit. The 48 V on-board electrical system battery and the DC/DC converter control unit communicate over the 48 V on-board electrical system LIN (LIN B22).

The drivetrain control unit evaluates all the relevant data, issues the corresponding stop enable and then switches off the engine. The drivetrain control unit then sends the "Drivetrain operational" signal over the chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit. This prevents the energy management system from reducing or switching off consumers if the "Engine running" signal is not sent.

If the air conditioning system automatic mode is active, the blower output is reduced. In high ambient temperatures the system changes into air circulation mode depending on the specified temperature adjusted.

After an engine stop, a maximum of three engine starts within one minute are permitted without exceeding the speed threshold of v = 8 km/h.

Engine start

The following events lead to an engine start-

The brake pedal is released (when the HOLD function is not active and the transmission position is D or N).
The accelerator pedal is operated.
The transmission mode is changed.
Reverse gear "R" is engaged.
Transmission position "P" is exited.
The vehicle moves off.
The temperature in the vehicle interior leaves the selected range.
The windshield is fogged (A/C system switched on).

Vehicles with code B01 (48V technology):

The 48 V on-board electrical system battery now supplies the energy required for the engine starting process.

The drivetrain control unit evaluates all relevant variables and starts the engine. Once the powertrain control unit detects an engine speed between 400 and 700 rpm, it ends the starting procedure and transmits the "Engine running" signal via the suspension FlexRay, electronic ignition lock control unit and interior CAN to the DC/DC converter control unit.

Vehicles except code B01 (48V technology):

By using the voltage dip limiter or starter front-end relay (series resistor) () at the positive terminal of the on-board electrical system battery, the voltage drop as perceived by the vehicle occupants when the engine is started (e.g. during radio or ventilation operation) is reduced.

The drivetrain control unit evaluates all relevant variables and starts the engine. Once the powertrain control unit detects an engine speed between 400 to 700 rpm, it ends the starting procedure and sends the "Engine running" signal over the suspension FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.

Forced engine start

To ensure that the on-board electrical system stability is also available during engine OFF, the powertrain control unit can also force the engine to start. A forced engine start is also conducted if, e.g. as a consequence of a request for load-intensive consumers, the on-board electrical system stability can no longer be assured.

The following events result in a forced engine start:

Brake Assist or the distance control is active.
The driver seat belt is released.
Driver door is open.
The ECO start/stop function is deactivated.

As soon as the energy management is no longer able to assure the stability of the 12-V on-board electrical system, or if one of the above mentioned events occurs, the front SAM control unit sends the "Start engine" request over the interior CAN, electronic ignition lock control unit and the chassis FlexRay to the powertrain control unit. The powertrain control unit then starts the engine.

If, following this, the on-board electrical system stability can still not be assured, the engine is no longer switched off. The ECO start/stop function is deactivated.

Vehicles with code B01 (48V technology)

As soon as the stability of the 48 V on-board electrical system is no longer assured, the drivetrain control unit starts the engine.

Vehicles except code B01 (48V technology):

The front SAM control unit uses the data from the battery sensor or the data from the control electronics in the on-board electrical system battery to calculate the alternator's specified voltage requirement and sends this over the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and the drive train CAN to the CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine). This makes the CDI control unit or the ME-SFI [ME] control unit start the alternator regulation (alternator management). For this purpose, the CDI control unit or the ME-SFI control unit evaluates the operating rate of the alternator (G2) and requests the corresponding specified voltage. The alternator and the CDI control unit or the ME-SFI [ME] control unit communicate with each other via the drive train LIN (LIN C1). The CDI control unit or the ME-SFI [ME] control unit also sends information on the alternator operating rate over the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.

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