ECO start/stop function energy management, function - GF54.10-P-1040RF

Model 205, 253 

The engine start/stop function is considered from the point of view of energy management.

Function requirements, general 

• Engine running and at operating temperature
• System diagnosis completed without errors
• Outside temperature T = -10 to 40 °C (except model 205.012/047/147/212/247) or T = -40 to 60 °C (model 205.012/047/147/212/247)
• On-board electrical system battery temperature (G1) T = 0 to 60 °C (except model 205.012/047/147/212/247) or T = -40 to 60 °C (model 205.012/047/147/212/247)
• On-board electrical system battery charged sufficiently

Energy management for engine start/stop, general 

Switching of the engine during standstill periods of the vehicle reduces the fuel consumption and therefore the carbon dioxide emissions. The master control unit for the engine start/stop function is the CDI control unit (N3/9) (diesel engine) or ME-SFI control unit (N3/10) (gasoline engine) which records and evaluates all influencing factors.

When the vehicle is stationary, the engine start/stop function switches off the engine automatically and, on vehicles with a conventional drive concept (except model 205.012/047/147/212/247), switches it on again as soon as the driver wants to drive off.

On vehicles with hybrid drive (model 205.012/047/147/212/247), 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 or the ME-SFI control unit starts the engine.

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

Vehicles with hybrid drive (model 205.012/047/147/212/247): 

By using the ECO start/stop function additional battery (G1/13), the voltage dip perceived by the vehicle occupants when the engine is started (e.g. during radio or ventilation operation) is prevented. The additional 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 additional battery is switched in by actuation of the ECO start/stop function additional 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 additional battery and disconnecting the on-board electrical system battery are functioning correctly.

Vehicles with conventional drive concept (except model 205.012/047/147/212/247): 

By using the voltage dip limiter (R62) (series resistor) at the positive terminal of the on-board electrical system battery, the tolerable voltage dip 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 dip in voltage when starting the engine.

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.

The engine start/stop function encompasses the following subfunctions:

• Function sequence for engine stop 
• Function sequence for engine start 
• Function sequence for forced engine start 
• Function sequence for determining state of the ECO start/stop function additional battery (model 205.012/047/147/212/247) 
• Function sequence for charging the ECO start/stop function additional battery (model 205.012/047/147/212/247) 

Additional function requirement for engine stop 

• Stop enable issued by the CDI control unit or the ME-SFI [ME] control unit

Function sequence for engine stop 

As the master control unit for the engine start/stop function, the CDI control unit or the ME-SFI [ME] control unit checks the 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 from the battery sensor (B95) (except CODE U98 (LITHIUM-ION STARTER BATTERY (LISB))) or the data from the control unit in the on-board electrical system battery (with CODE U98 (LITHIUM-ION STARTER BATTERY (LISB))) via the battery sensor LIN (LIN B15), evaluates it and sends information describing the status of the on-board electrical system and the requirements via the interior CAN (CAN B), electronic ignition lock control unit (N73), chassis FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1) to the CDI control unit or ME-SFI control unit.

The following information is included in it:

• State of on-board electrical system battery
• State of ECO start/stop function additional battery (model 205.012/047/147/212/247)
• On-board electrical system status

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, powertrain 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 205.012/047/147/212/247

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 the engine has been switched off a maximum of three engine starts within a period of t = 1 minute (maximum idle time t = 180 s) with exceeding the speed threshold of v = 8 km/h are permitted.

Function sequence for engine start 

The following events result in 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 rolls off.
• The temperature in the vehicle interior moves outside of the set range.
• The windshield fogs up (air conditioning switched on).

Vehicles with hybrid drive (model 205.012/047/147/212/247): 

During the starting procedure the on-board electrical system battery is isolated from the on-board electrical system. The ECO start/stop function additional battery then supplies all active electrical consumers. This serves to prevent any voltage dip as perceived 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 additional battery relay and the decoupling relay.

The additional 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 solely provided by the ECO start/stop function additional battery. 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, powertrain 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 additional battery relay directly.

The decoupling relay connects the on-board electrical system battery to the on-board electrical system. The additional battery relay for ECO start/stop function disconnects the additional 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 205.012/047/147/212/247): 

By using the voltage dip limiter (series resistor) at the positive terminal of the on-board electrical system battery, the tolerable voltage dip 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, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.

Function sequence for forced engine start 

To ensure that the on-board electrical system stability is also given during engine OFF, the CDI control unit or the ME-SFI [ME] control unit 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.
• The driver seat belt is released.
• Driver door open.
• The Brake Assist System or distance control are activated.

Model 205.012/047/147/212/247

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.

As soon as the energy management system is no longer able to ensure the stability of the on-board electrical system, the front SAM control unit sends the "Start engine" request via the interior CAN, electronic ignition lock control unit, suspension FlexRay, powertrain control unit and the drive train CAN to the CDI control unit or to the ME-SFI control unit. The CDI control unit or the ME-SFI 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 engine start/stop function is deactivated.

The front SAM control unit uses the data from the battery sensor or the data from the control unit in the on-board electrical system battery to calculate the required alternator voltage and sends this via the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit, and drive train CAN to the CDI control unit or ME-SFI [ME] control unit. This makes the CDI control unit or the ME-SFI 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 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.

Function sequence for determining state of the ECO start/stop function additional battery (model 205.012/047/147/212/247) 

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 additional 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 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 additional 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 additional battery for ECO start/stop function

In order to establish this, the voltage of the ECO start/stop function additional battery is compared with 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.

Function sequence for charging the ECO start/stop function additional battery (model 205.012/047/147/212/247) 

The charging strategy of the ECO start/stop function additional battery must take into account two criteria:

• The ECO start/stop function additional battery must always be sufficiently charged.
• The number of additional battery relay for the ECO start/stop function actuations and the related load on the additional battery for the ECO start/stop function must be minimized as far as possible.

If the voltage dip at engine start is too great (U < 11 V), an engine stop is not permitted for t = 1 min in order to recharge the additional battery for the ECO start/stop function. The additional battery for the ECO start/stop function is only switched in when alternator management is not 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.

	Electrical function schematic for energy management for engine start/stop		PE54.10-P-2070-97FBA
	Overview of energy management system components		GF54.10-P-9990RF