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

Model 213 up to model year 2021 

Function requirements, general 

• Engine running and at operating temperature
• System diagnosis completed without errors
• Outside temperature -10 to 40°C (except model 213.016/050/053/054/216) or -40 to 60°C (model 213.016/050/053/054/216)
• Temperature of on-board electrical system battery (G1) 0 to 60°C (except model 213.016/050/053/054/216) or -40 to 60°C (model 213.016/050/053/054/216)
• 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 engine start/stop function is the powertrain control unit (N127), that records and evaluates all influencing factors.

When the vehicle is stationary, the ECO start/stop function automatically switches off the engine and, on vehicles with a conventional drive concept (except model 213.016/050/053/054/216), switches it on again as soon as the driver wants to drive off.

On vehicles with hybrid drive (model 213.016/050/053/054/216), the vehicle drives off using electric power only, 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 (N3/9) or the ME-SFI [ME] control unit (N3/10) starts the engine.

Model 213.016/050/053/054/216 up to model year 2021

Detailed information on the hybrid system is available in a separate function description.

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

Vehicles with hybrid drive (model 213.016/050/053/054/216): 

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 additional battery for the ECO start/stop function is activated by actuation of the ECO start/stop function additional battery relay (K114). The on-board electrical system battery is decoupled from the on-board electrical system by actuating the ECO start/stop function diode (V19) at the positive terminal on the on-board electrical system battery. The front SAM control unit (N10/6) also checks the function of the components involved in disconnecting the on-board electrical system battery and switching on the ECO start/stop function additional battery.

Vehicles with conventional drive concept (except model 213.016/050/053/054/216) and except code B01 (48V technology): 

By using the voltage dip limiter (R62) (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 voltage dip limiter reacts to the drop in voltage when the engine is started.

The voltage dip limiter is an electronically switchable series resistor for reducing the high power consumption of the starter (M1) when the engine is started, and is connected via circuit 87 to the starter relay of circuit 50 (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. If the on-board electrical system voltage reduces too much due to the high power consumption of the starter, the voltage dip limiter switches the series resistor out again.

Vehicles with code B01 (48V technology): 

The 48 V on-board electrical system provides the energy for the starting procedure. 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 condition of ECO start/stop function auxiliary battery (model 213.016/050/053/054/216) 
• Charge ECO start/stop function auxiliary battery (model 213.016/050/053/054/216) 

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 reads in the data of the battery sensor (B95) via the battery sensor LIN (LIN B15), evaluates the data and sends information describing the condition or the load requests to the 12 V on-board electrical system, via the interior CAN (CAN B), electronic ignition lock control unit (N73) and the suspension FlexRay (Flex E) to the powertrain control unit. On vehicles with hybrid drive (model 213.016/050/053/054/216) this information also includes the status of the auxiliary battery for the ECO start/stop function.

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 setting is reduced. In high ambient temperatures the system changes into air circulation mode depending on the specified temperature adjusted.

Model 213.016/050/053/054/216 up to model year 2021

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 HOLD function is not active and transmission is in position D or N (transmission 725)).
• The accelerator pedal is operated (transmission 725).
• The transmission mode is changed (transmission 725).
• Reverse gear "R" is engaged (transmission 725).
• The transmission is shifted out of position "P" (transmission 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 213.016/050/053/054/216): 

During the starting procedure the on-board electrical system battery is isolated from the on-board electrical system. The power supply for the active consumers is now provided by the additional battery for the ECO start/stop function. 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 the hot start signal over a direct line and actuates the ECO start/stop function additional battery relay and the ECO start/stop function diode. The auxiliary battery for the ECO start/stop function is then switched through to the on-board electrical system. The ECO start/stop function diode disconnects the on-board electrical system battery from the on-board electrical system during the starting procedure. The energy requirement of the on-board electrical system is now solely provided by the ECO start/stop function auxiliary battery. The on-board electrical system battery now supplies the energy required for the engine starting process.

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. The front SAM control unit then actuates the ECO start/stop function diode and the additional battery relay for the ECO start/stop function.

The ECO start/stop function diode then switches the on-board electrical system battery through 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 conventional drive concept (except model 213.016/050/053/054/216) and except code B01 (48V technology): 

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 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 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.

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 also lead to 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.

Model 213.016/050/053/054/216

up to model year 2021

The engine can also 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.

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) and except model 213.016/050/053/054/216: 

The front SAM control unit uses the data from the battery sensor as the basis for determining the required alternator voltage, 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 or to the ME-SFI [ME] control unit. 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.

Determine condition of ECO start/stop function auxiliary battery (model 213.016/050/053/054/216) 

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 additional battery for ECO start/stop function in an active ECO start/stop function 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:

• Additional battery for ECO start/stop function deep discharged
• Internal short circuit
• Short circuit in positive line of auxiliary battery for ECO start/stop function

A corresponding fault message is indicated in 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 ECO start/stop function auxiliary battery (model 213.016/050/053/054/216) 

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 one minute so as to allow recharging of the ECO start/stop function auxiliary battery. The ECO start/stop function auxiliary battery is only switched in when 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.

	Electrical function schematic for energy management, ECO start/stop function		PE54.10-P-2075-97DBA
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