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

Model 217, 222 

Function requirements, general 

• Engine running and at operating temperature
• System diagnosis completed
• Outside temperature T = -10 to 40°C (except model 222.004/057/104/157/163/173) or T = -40 to 60°C (model 222.004/057/104/157/163/173)
• Battery temperature T = 0 to 60°C (except model 222.004/057/104/157/163/173) or T = -40 to 60°C (model 222.004/057/104/157/163/173)
• On-board electrical system battery charged sufficiently

Energy management for engine start/stop, 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 engine start/stop function switches off the engine automatically and, on vehicles with a conventional drive concept (except model 222.004/057/104/157/163/173), switches it on again as soon as the driver wants to drive off.

On vehicles with hybrid drive (model 222.004/057/104/157/163/173), 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 222.004/057/104/157/163/173

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.

On vehicles except code B01 (48V technology) 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 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 (G1) 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 on by actuating the ECO start/stop function auxiliary battery relay (F33k2) in the rear prefuse box (F33). The on-board electrical system battery is disconnected from the on-board electrical system through actuation of the decoupling relay (F33k1).

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. Immediately after the cold start of the engine, the powertrain control unit runs a system diagnosis and evaluates the functional capability of the engine start/stop function. On vehicles except code B01 (48V technology), the front SAM control unit (N10/6) checks the function of the components involved for decoupling the on-board electrical system battery and switching in the ECO start/stop function auxiliary battery.

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 status of ECO start/stop function auxiliary battery (except code B01 (48V technology)) 
• Function sequence for charging ECO start/stop function auxiliary battery (except code B01 (48V technology)) 

Additional function requirement for engine stop 

• Stop enable issued by powertrain control unit

Function sequence for engine stop 

As the master control unit for the engine 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.

On vehicles except code B01 (48V technology), the CDI control unit or the ME-SFI [ME] control unit evaluates the operating rate of the alternator (G2) while the engine is running. 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 ME-SFI [ME] control unit then sends the "engine running" signal and information regarding the operating rate of the alternator via the powertrain CAN (CAN C1), powertrain control unit (N127), chassis FlexRay (Flex E), electronic ignition lock control unit (N73) and interior CAN (CAN B) to the front SAM control unit.

The front SAM control unit reads in the data from the battery sensor (B95) (except engine 157, 279) or the data from the control unit in the on-board electrical system battery (engine 157, 279) over the battery sensor LIN (LIN B15), evaluates the condition of the on-board electrical system battery and sends information that describes the state of the on-board electrical system or the requests to the on-board electrical system, over the interior CAN, electronic ignition lock control unit and the suspension FlexRay 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 powertrain 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 powertrain control unit evaluates all the relevant data, issues the corresponding stop enable and then switches off the engine. The powertrain 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.

When the vehicle is stationary, the brake pedal must be pressed and held or the "Hold" function must be active. The blower setting is reduced when the automatic blower speed function of the air conditioning is active. In high ambient temperatures the system changes into air circulation mode depending on the specified temperature adjusted.

Model 222.004/057/104/157/163/173

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).

Following an engine stop a maximum of three engine starts is permitted within a period of t = 1 min. without exceeding the speed threshold of v = 8 km/h.

Function sequence for 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 powertrain control unit evaluates all relevant variables and starts the engine. As soon as the powertrain 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 except code B01 (48V technology): 

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 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 auxiliary battery. This serves to prevent any voltage drop being noticed by vehicle occupants when starting the engine (e.g. during radio or ventilation operation). The on-board electrical system battery now supplies the energy required for the engine starting process.

As soon as the powertrain 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 decoupling relay and the ECO start/stop function auxiliary battery relay directly.

The decoupling relay reconnects 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.

Function sequence for 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, as a consequence of load-intensive consumers, the on-board electrical system stability can no longer be assured.

The following results force an engine start:

• The ECO start/stop function is switched off (except model 222.004/057/104/157/163/173).
• The driver seat belt is released.
• Driver door is open.
• Brake Assist or the distance control is active.

Model 222.004/057/104/157/163/173

The engine can also be forced to start as part of system optimization. For example if the charge level of the high-voltage battery drops below a defined threshold value.

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 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 powertrain control unit starts the engine.

Vehicles except code B01 (48V technology): 

The front SAM control unit uses the data from the battery sensor (except engine 157, 279) or the data from the control unit in the on-board electrical system battery (engine 157, 279) to calculate the required alternator specified voltage and sends this via the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and powertrain CAN to the CDI control unit or 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 [ME] control unit assesses the operating rate of the alternator and requests the corresponding specified voltage (excitation voltage). The alternator and the CDI control unit or the ME-SFI [ME] control unit communicate with each other via the drive train LIN. The CDI control unit or the ME-SFI [ME] control unit then sends information on the alternator operating rate via the powertrain 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 status of ECO start/stop function auxiliary battery (except code B01 (48V technology)) 

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 at the additional battery for the ECO start/stop function is checked 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

To determine this, the voltage for the ECO start/stop function auxiliary battery is compared against a stored value. 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.

Function sequence for charging ECO start/stop function auxiliary battery (except code B01 (48V technology)) 

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 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 drop at engine start is too large (U <11 V), an engine stop is not permitted for t = 1 min., to recharge the ECO start/stop function auxiliary battery. The ECO start/stop function auxiliary battery is only connected when the alternator management is inactive, and the on-board electrical system voltage (U > 13 V) is high enough. 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-2070-97SEA
	Overview of energy management system components		GF54.10-P-9990LF