ECO Start/Stop Function Energy Management, Function - GF54.10-P-1040RF
Model 205, 253 (except 253.99)
Function requirements, general
- Engine running and at operating temperature
- System diagnosis completed without errors
- Outside temperature T = -10 up to 40°C (except hybrid vehicle) or T = -40 up to 60°C (hybrid vehicle)
- On-board electrical system battery temperature (G1) T = 0 to 60°C (except hybrid vehicle) or T = -40 to 60°C (hybrid vehicle)
- 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 of the ECO start/stop function is the CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine) (model 205 up to 31.05.2018, model 253 up to 31.05.2019) or the powertrain control unit (N127) (model 205 as of 01.06.2018, model 253 as of 01.06.2019) that detects and evaluates all influencing factors.
When the vehicle is stationary, the ECO start/stop function automatically switches off the engine and starts it again in vehicles with conventional drive concept (except hybrid vehicle) once the driver wants to drive off.
In vehicles with hybrid drive, the vehicle drives away in electric-only mode depending on the charge level of the high-voltage battery (A100g1). If the charge level of the high-voltage battery is below 30 %, the CDI control unit or the ME-SFI [ME] control unit starts the engine.
It is still possible to stop and start the engine in the conventional way.
Vehicles with hybrid drive:
By using the ECO start/stop function auxiliary battery (G1/13), the voltage drop perceived by the vehicle occupants when the engine is started (e.g. during radio or ventilation operation) is prevented. The auxiliary battery for ECO start/stop function then assumes the power supply for the active consumers in the process while the on-board electrical system battery is isolated from the on-board electrical system (at engine start). Active comfort functions are not switched off. The ECO start/stop function auxiliary battery is switched in by actuation of the ECO start/stop function auxiliary battery relay (K114). The on-board electrical system battery is disconnected from the on-board electrical system by actuating the decoupling relay (F32/3k1) in the engine compartment prefuse box (F32/3).
The front SAM control unit (N10/6) continuously checks that all components involved in switching in the ECO start/stop function auxiliary battery and disconnecting the on-board electrical system battery are functioning correctly.
Vehicles with conventional drive concept (except vehicles with code B01 (48V technology)):
The use of the voltage dip limiter (R62) at the positive pole of the on-board electrical system battery, enables the voltage drop perceived by the vehicle occupants when the engine is started (e.g. during radio or ventilation mode) to be reduced. The voltage dip limiter is a series resistor that can be switched on and off electronically.
The voltage dip limiter reduces the power consumption of the starter (M1) when the engine is started and is connected via circuit 87 to the circuit 50 starter relay (K40/8kH). When starting the engine, the voltage dip limiter is exposed to voltage. It thereby detects the starting procedure and switches in the series resistor. After completion of the starting procedure the voltage dip limiter switches off 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
- Determine status of auxiliary battery of ECO start/stop function (hybrid vehicle)
- Charge auxiliary battery OF ECO start/stop function (hybrid vehicle)
Additional function requirement for engine stop
- Stop enable issued by CDI control unit or by ME-SFI [ME] control unit (model 205 up to 31.05.2018, model 253 up to 31.05.2019)
- Stop enable issued by powertrain control unit (model 205 as of 01.06.2018, model 253 as of 01.06.2019)
Engine stop
As the master control unit of the ECO start/stop function, the CDI control unit or the ME-SFI [ME] control unit (model 205 up to 31.05.2018, model 253 up to 31.05.2019) or the powertrain control unit (model 205 as of 01.06.2018, model 253 as of 01.06.2019) checks the different influencing factors for 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 reads in the data from the battery sensor (B95) over the battery sensor LIN (LIN B15), evaluates the data and then sends information that describes the status or load requirements of the 12 V on-board electrical system, over the interior CAN (CAN B), electronic ignition lock control unit (N73) and suspension FlexRay (Flex E) to the drivetrain control unit. For model 205 up to 31.05.2018 and model 253 up to 31.05.2019, the powertrain control unit transmits this information via the drive CAN (CAN C1) to the CDI control unit or the ME-SFI [ME] control unit.
The following information is included in it:
- State of on-board electrical system battery
- Status of auxiliary battery of ECO start/stop function (hybrid vehicle)
- Status of on-board electrical system (consumer load)
- Temperature of on-board electrical system battery
- Outside temperature
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).
Model 205 as of 01.06.2018, model 253 as of 01.06.2019:
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.
Model 205 up to 31.05.2018, model 253 up to 31.05.2019:
The CDI control unit or the ME-SFI [ME] control unit evaluates all the relevant data, issues the stop enable and switches the engine off. The CDI control unit or the ME-SFI [ME] control unit then sends the "Drive train operational" signal over the drive train CAN, drivetrain control unit, 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.
Model 205.012/013/047/053/147/212/213/247/253, 253.311/353/354/911/953/954
The engine can also be stopped as part of system optimization. The kinetic energy can then, for example, be converted into electrical energy (regenerative braking).
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 clutch pedal is operated (transmission 716).
- The brake pedal is released (if the HOLD function is not active and the transmission position is in D or N (transmission 722, 724, 725)).
- The accelerator pedal is actuated (transmission 722, 724, 725).
- The transmission mode is changed (transmission 722, 724, 725).
- Reverse gear "R" is engaged (transmission 722, 724, 725).
- The transmission is moved out of transmission position "P" (transmission 722, 724, 725).
- 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 hybrid drive, model 205 as of 01.06.2018, model 253 as of 01.06.2019:
During the starting procedure the on-board electrical system battery is isolated from the on-board electrical system. The ECO start/stop function auxiliary battery then powers all the active electrical consumers. This serves to prevent any voltage drop being noticed by vehicle occupants when starting the engine (e.g. during radio or ventilation operation).
The drivetrain control unit evaluates all relevant variables and issues the start enable (hot start signal). The front SAM control unit reads in this hot-start signal via a direct line and directly actuates the ECO start/stop function auxiliary battery relay and the decoupling relay.
The auxiliary battery for the ECO start/stop function is then switched through to the on-board electrical system. The decoupling relay isolates the on-board electrical system battery from the on-board electrical system for the duration of the starting procedure. The energy requirement of the on-board electrical system is now primarily powered by the auxiliary battery for the ECO start/stop function. The on-board electrical system battery now supplies the energy required for the engine starting process.
Once the drivetrain control unit detects an engine speed of n = 400 to 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 front SAM control unit. The front SAM control unit then actuates the decoupling relay and the ECO start/stop function auxiliary battery relay directly.
The decoupling relay connects the on-board electrical system battery to the on-board electrical system. The auxiliary battery relay for ECO start/stop function disconnects the auxiliary battery for ECO start/stop function from the on-board electrical system. The energy requirement of the on-board electrical system is now supplied again by the on-board electrical system battery.
Vehicles with hybrid drive, model 205 up to 31.05.2018, model 253 up to 31.05.2019:
During the starting procedure the on-board electrical system battery is isolated from the on-board electrical system. The ECO start/stop function auxiliary battery then powers all the active electrical consumers. This serves to prevent any voltage drop being noticed by vehicle occupants when starting the engine (e.g. during radio or ventilation operation).
The CDI control unit or the ME-SFI [ME] control unit evaluates all relevant influencing factors and then issues the start enable (hot start signal). The front SAM control unit reads in this hot-start signal via a direct line and directly actuates the ECO start/stop function auxiliary battery relay and the decoupling relay.
The auxiliary battery for the ECO start/stop function is then switched through to the on-board electrical system. The decoupling relay isolates the on-board electrical system battery from the on-board electrical system for the duration of the starting procedure. The energy requirement of the on-board electrical system is now primarily powered by the auxiliary battery for the ECO start/stop function. The on-board electrical system battery now supplies the energy required for the engine starting process.
As soon as the CDI control unit or the ME-SFI [ME] control unit detects an engine speed of n = 400 to 700 rpm, it stops the starting procedure and sends the "Engine running" signal over the drive train CAN, drivetrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit. The front SAM control unit then actuates the decoupling relay and the ECO start/stop function auxiliary battery relay directly.
The decoupling relay connects the on-board electrical system battery to the on-board electrical system. The auxiliary battery relay for ECO start/stop function disconnects the auxiliary battery for ECO start/stop function from the on-board electrical system. The energy requirement of the on-board electrical system is now supplied again by the on-board electrical system battery.
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. As soon as the drivetrain control unit recognizes an engine speed of 400 to 700 rpm, it ends the start procedure and sends the "Engine running" signal over the suspension FlexRay, electronic ignition lock control unit and the interior CAN to the DC/DC converter control unit.
Vehicles with a conventional drive concept (except code B01 (48V technology)), model 205 as of 01.06.2018, model 253 as of 01.06.2019:
The use of the voltage dip limiter (series resistor) at the positive pole of the on-board electrical system battery, enables the voltage drop perceived by the vehicle occupants when the engine is started (e.g. during radio or ventilation mode) to be reduced.
The drivetrain control unit evaluates all relevant variables and starts the engine. As soon as the drivetrain control unit recognizes an engine speed of 400 to 700 rpm, it ends the start procedure and sends the "Engine running" signal over the chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.
Vehicles with conventional drive concept, model 205 up to 31.05.2018, model 253 up to 31.05.2019:
By using the voltage dip limiter (series resistor) at the positive terminal of the on-board electrical system battery, the perceivable voltage drop for the vehicle occupants when starting the engine (e.g. during operation of the radio or ventilation mode) is reduced.
The CDI control unit or the ME-SFI control unit evaluates all relevant variables and starts the engine. As soon as the CDI control unit or the ME-SFI [ME] control unit detects an engine speed of n = 400 to 700 rpm, it stops the starting procedure and sends the "Engine running" signal over the drive train CAN, drivetrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.
Forced engine start
To ensure the stability of the on-board electrical system also during engine off, the CDI control unit or the ME-SFI [ME] control unit (model 205 up to 31.05.2018, model 253 up to 31.05.2019) or the powertrain control unit (model 205 as of 01.06.2018, model 253 as of 01.06.2019) can also force the engine to start. A forced engine start is also conducted if, as a consequence of load-intensive consumers, the on-board electrical system stability can no longer be assured.
The following events result in a forced engine start:
- The ECO start/stop function is switched off.
- Brake Assist or the distance control is active.
Model 205.012/013/047/053/147/212/213/247/253, 253.311/353/354/911/953/954
The engine can be forced to start as part of system optimization. For example when the charge level of the high-voltage battery drops below a defined limit.
Once the energy management can no longer ensure the stability of the 12 V on-board electrical system or one of the above-mentioned events occurs, the front SAM control unit transmits the request "Start engine" via the interior CAN, electronic ignition lock control unit, suspension FlexRay to the drivetrain control unit. For model 205 up to 31.05.2018 and model 253 up to 31.05.2019, the powertrain control unit transmits this information via the drive CAN to the CDI control unit or the ME-SFI [ME] control unit. The powertrain control unit (model 205 as of 01.06.2018, model 253 as of 01.06.2019) or the CDI control unit or the ME-SFI [ME] control unit (model 205 up to 31.05.2018 and model 253 up to 31.05.2019) 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 switched off.
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.
Determine status of auxiliary battery of ECO start/stop function (hybrid vehicle)
The front SAM control unit runs a battery state recognition immediately after the engine is started. This provides information regarding the availability of electrical power to the auxiliary battery for the ECO start/stop function. If the engine is switched off during the battery state recognition, the SAM control unit switches this off and discards the previous results.
In addition to battery state recognition, the voltage of the auxiliary battery for ECO start/stop function mode in the start-stop function mode is tested after every engine start.
The battery state recognition can be started using a diagnosis tester.
The auxiliary battery relay for the ECO start/stop function is no longer actuated under the following conditions:
- Auxiliary battery for the ECO start/stop function deep discharge (U < 6 V)
- Internal short circuit
- Short circuit in positive line of auxiliary battery for ECO start/stop function
To determine this, the voltage for the ECO start/stop function auxiliary battery is compared against a stored value. A corresponding fault message is shown in the multifunction display (A1p13) of the instrument cluster (A1). The front SAM control unit sends the data required for this over the interior CAN, electronic ignition lock control unit and user interface CAN (CAN HMI) to the instrument cluster.
Charge auxiliary battery OF ECO start/stop function (hybrid vehicle)
The charging strategy of the ECO start/stop function auxiliary battery must take into account two criteria:
- The ECO start/stop function auxiliary battery must always be sufficiently charged.
- The number of auxiliary battery relay for the ECO start/stop function actuations and the related load on the auxiliary battery for the ECO start/stop function must be minimized as far as possible.
If the voltage drop at engine start is too large (U < 11 V), an engine stop is not permitted for t = 1 min. in order to recharge the auxiliary battery for the ECO start/stop function. The auxiliary battery for the ECO start/stop function is only switched in when no alternator management is active and the on-board electrical system voltage is high enough (U > 13 V). It is disconnected again when the alternator management is active or the on-board electrical system is severely overloaded.
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