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

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MODEL 212 as of model year 2014

The function "Engine start/stop energy management, function" is viewed from an energy management point-of-view. Information on the function "Engine timing, start/stop function" is documented in the function description "Common rail diesel injection (CDI), function" (diesel engine) or "Gasoline injection and ignition system with direct injection, function" (gasoline engine).

Function requirements, general

Engine running and at operating temperature
Engine hood closed
One-time overspeeding of v = 15 km/h in forward travel
System diagnosis completed
Outside temperature T = -10 to 40 °C (except model 212.095/098/298) or T = -40 to 60 °C (model 212.095/098/298)
Battery temperature T = 0 to 60 °C (except model 212.095/098/298) or T = -40 to 60 °C (model 212.095/098/298)
A/C regulated

Energy management for engine start/stop, general

For a stationary vehicle, the engine Start-Stop function switches the engine off automatically and starts it again, as soon as the driver wishes to drive off.

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.

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

Vehicles up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version):

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 ECO start/stop function additional battery then supplies power for the active consumers while the on-board electrical system battery (G1) is disconnected from the on-board electrical system (during engine start). Active comfort functions are not switched off.

The additional battery for ECO start/stop function is actuated by the additional battery relay for ECO start/stop function (K114). For vehicles with manual transmission, this is designed as a mechanical relay and for vehicles with automatic transmission as an electronic relay.

On vehicles with manual transmission, the on-board electrical system battery is decoupled from the on-board electrical system by means of the on-board electrical system decoupling relay (K19/7) and, on vehicles with automatic transmission, by means of the ECO start/stop function diode (V19).

In addition, the front SAM control unit with fuse and relay module (N10/1) checks that all components involved in isolating the on-board electrical system battery and connecting the ECO start/stop function additional battery are functioning correctly.

Vehicles as of 01.12.2014 except engine 642 and except CODE 460 (Canada version) and except CODE 494 (USA version):

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 that is used to reduce the high power consumption of the starter (M1) when starting the engine; it is connected via circuit 87 to the circuit 50 starter relay (N10/1kM). When the engine is started by the CDI control unit or the ME-SFI control unit, voltage is applied to the voltage dip limiter. 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 status of ECO start/stop function additional battery (up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version))
Function sequence for charging ECO start/stop function additional battery (up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version))

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.

Model 212 except model 212.095:

While the engine is running, the CDI control unit or ME-SFI control unit assesses the operating rate of the alternator (G2). 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 control unit then sends the "engine running" signal and information on the operating rate of the alternator via chassis CAN 1 (CAN E1), the front SAM control unit and the interior CAN (CAN B) to the rear SAM control unit with fuse and relay module (N10/2).

Model 212.095/098/298:

While the engine is running, the CDI control unit or the ME-SFI control unit evaluates the operating rate of the power electronics control unit (N129/1), which controls the energy transfer from the high-voltage on-board electrical system to the 12 V on-board electrical system. The power electronics control unit and the CDI control unit or ME-SFI control unit communicate with each other via the hybrid CAN (CAN L). The CDI control unit or the ME-SFI control unit then sends the "engine running" signal and information on the operating rate of the power electronics control unit via chassis CAN 1, the front SAM control unit and interior CAN to the rear SAM control unit.

The rear SAM control unit receives the respective information, reads in the data from the battery sensor (B95) via the on-board electrical system LIN (LIN B7), evaluates the state of the on-board electrical system battery and sends information that describes the state of the on-board electrical system or the requirements with regard to the on-board electrical system, via the interior CAN, front SAM control unit and chassis CAN 1 to the CDI control unit or ME-SFI control unit.

The CDI control unit or the ME-SFI [ME] control unit evaluates all the relevant data and then issues the stop enable. The engine is switched off as a result of this. The CDI control unit or the ME-SFI control unit then sends the "Drive train operational" signal to the rear SAM control unit via chassis CAN 1, the front SAM control unit and interior CAN.

This prevents the energy management system from reducing or switching off consumers if the "Engine running" signal is not sent. The blower output 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.

After an engine stop a maximum of three engine starts is permitted without exceeding the speed threshold of v = 8 km/h.

Function sequence for engine start

Depressing the clutch (transmission 711, 716) or the accelerator pedal (transmission 722, 724, 725) starts the engine.

Vehicles up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version):

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 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 actuates the on-board electrical system decoupling relay (manual transmission) or the ECO start/stop function diode (automatic transmission) and the ECO start/stop function additional battery relay.

The additional battery for the ECO start/stop function is then switched through to the on-board electrical system. Shortly after this the on-board electrical system decoupling relay (manual transmission) or the ECO start/stop function diode (automatic transmission) disconnects the on-board electrical system battery from the on-board electrical system during the start procedure.

As soon as the CDI control unit or the ME-SFI control unit detects an engine speed of n = 400 to 700 rpm, it stops the starting procedure and sends the "engine running" signal via chassis CAN 1 to the front SAM control unit. As a result of this the front SAM control unit actuates the decoupling relay for on-board electrical system (manual transmission) or the diode for the ECO start/stop function (A/T) and the additional battery relay for ECO start/stop function. The decoupling relay for on-board electrical system (manual transmission) or the diode for ECO start/stop function (A/T) 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 as of 01.12.2014 except engine 642 and except CODE 460 (Canada version) and except CODE 494 (USA version):

The voltage dip limiter at the positive terminal of the on-board electrical system battery reacts to the voltage dip when the engine is started (circuit 87) by the CDI control unit or ME-SFI control unit and switches in an electronic series resistor for a certain time and then switches it out again. This reduces the high power draw from the on-board electrical system battery and therefore the voltage dip perceived by the vehicle occupants when the engine is started (e.g. during radio or ventilation operation).

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 E-SFI control unit detects an engine speed of n = 400 to 700 rpm, it stops the starting procedure and sends the "engine running" signal via chassis CAN 1 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 systems can cause a critical voltage value and therefore trigger a forced engine start:

Air conditioning
Steering

On model 212.095, the ME-SFI control unit sends the request of the rear SAM control unit via the hybrid-CAN to the power electronics control unit. The power electronics control unit then controls the energy transfer from the high-voltage on-board electrical system. The ME-SFI control unit then evaluates the operating rate of the power electronics control unit and sends information about the operating rate via chassis CAN 1, the front SAM control unit and interior CAN to the rear SAM control unit.

Detailed information about alternator regulation can be found in the separate function "Engine ON energy management, function".

As soon as the energy management is no longer able to ensure the stability of the on-board electrical system, the rear SAM control unit sends an engine start request via the interior CAN (CAN B), front SAM control unit and chassis CAN 1 to the CDI control unit or to the ME-SFI control unit. The CDI control unit or the ME-SFI [ME] control unit receives this and 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 prevented temporarily.

The rear SAM control unit uses the data from the battery sensor (except model 212.095) to calculate the required alternator specified voltage and the required energy transfer from the DC/DC converter in the power electronics control unit (model 212.095/098/298) and sends corresponding requests via the interior CAN, front SAM control unit and chassis CAN 1 to the CDI control unit and to the ME-SFI control unit. The CDI control unit or the ME-SFI control unit then starts alternator regulation (alternator management) (except model 212.095). For this purpose, the CDI control unit or the ME-SFI 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 control unit communicate with each other via the drivetrain LIN. The CDI control unit or the ME-SFI control unit then sends information about the operating rate of the alternator to the rear SAM control unit via chassis CAN 1, the front SAM control unit and interior CAN.

Illustration showing principle of power supply at engine start (vehicles up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version))

Fig 1: Engine Start Power Supply Circuit Diagram

Courtesy of MERCEDES-BENZ USA

Illustration showing principle of power supply with engine running (vehicles up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version))

Fig 2: Engine Running Power Supply Circuit Diagram

Courtesy of MERCEDES-BENZ USA

Function sequence for determining status of ECO start/stop function additional battery (up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version))

The front SAM control unit performs battery state recognition immediately after the engine is started, and sends the result via the interior CAN to the rear SAM control unit. 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 battery state recognition, the front SAM control unit stops battery state recognition and discards the results so far collected.

Battery state recognition can be started using the diagnostic tester. In addition to battery state recognition, the front SAM control unit checks the voltage at the ECO start/stop function additional battery in the start/stop mode after each engine start.

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 at the ECO start/stop function additional battery is compared with an internal value.

A corresponding fault message is shown in the multifunction display (A1p13) of the IC (A1). The front SAM control unit transmits the data required for this to the instrument cluster via the interior CAN.

Function sequence for charging ECO start/stop function additional battery (up to 30.11.2014 and as of 01.12.2014 with engine 642 and with CODE 460 (Canada version) or CODE 494 (USA version))

The ECO start/stop function additional battery is charged by means of actuation of the ECO start/stop function additional battery relay.

The charging strategy of the additional battery for ECO start/stop unction must take two requirements into account:

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 open circuit voltage of the ECO start/stop function additional battery is too low, the output limitation of the alternator (alternator management) (except model 212.095) is deactivated or a higher energy transfer from the high-voltage on-board electrical system (model 212.095) is requested so that the ECO start/stop function additional battery can be charged. For this purpose, the rear SAM control unit sends the "Actuate ECO start/stop function additional battery relay" request via the interior CAN to the front SAM control unit. If the voltage dip at engine start is too great, an engine stop is deactivated for = 1 min in order to recharge the ECO start/stop function additional battery.

The ECO start/stop function additional battery is only switched in if no output limitation of the alternator is active (except model 212.095) or the energy transfer from the high-voltage on-board electrical system is sufficient (model 212.095) and the on-board electrical system voltage is high enough. It is switched out again if the on-board electrical system is severely overloaded.

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