Engine Start/Stop Automatic Function - GF54.10-P-1070KJ

MODEL 453.0 (except 453.091), 453.3 (except 453.391), 453.4 (except 453.491) with CODE B03 (ECO start/stop function) 

The "automatic engine start/stop function" is seen from the point of view of the engine management. Information on the "engine management start-stop function" is available in the function description for the "gasoline injection and ignition system with direct injection function".

General function requirements 

• Engine running and at operating temperature (coolant temperature T > 21°C < 105°C)
• Liftgate closed
• Outside temperature T = 0 to 40°C (with code I01 (Automatic air conditioning)); T = 0 to 35°C (without code I01 (Automatic air conditioning))
• On-board electrical system battery sufficiently charged > 80 %
• System diagnosis completed
• Indicator lamp (LED) of automatic start/stop button is not lit
• No fogging due to moisture on the windshield
• Driver door closed
• Driver-side seat belt buckle switch closed

Automatic 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 start/stop function is the driver-side SAM control unit (N10/11). It registers all influencing factors and evaluates them.

When the vehicle is stationary, the start/stop function switches the engine off automatically and starts it again when the driver commands it.

It is still possible to start the engine in the conventional way with the ignition key.

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 

Additional function requirements for engine stop 

• Stop enable from driver-side SAM control unit

Function sequence for automatic engine stop 

The engine stop function is available for vehicles with manual transmission (code 410 (Manual transmission, 5-speed))  , if:

• The function is activated (start/stop button),
• AND the clutch is not depressed,
• AND the transmission is in neutral (for an automatic stop to be authorized, a shift from a gear to neutral must have been detected),
• AND the vehicle speed is below v = 3 km/h,
• AND the vehicle speed has reached at least 10 km/h since the last time reverse gear was engaged.

The engine stop function is available for vehicles with automatic transmission (code 429 (twinamic))  , if:

• The function is activated (start/stop button),
• Gear ranges are D, N and M at vehicle speed v = 0 km/h and the accelerator pedal has not been depressed for approx. 1.5 s,
• Gear range is P at vehicle speed v = 0 km/h and the accelerator pedal not depressed,
• Gear range is N with parking brake applied, at vehicle speed v = 0 km/h and accelerator pedal not depressed,
• AND the vehicle speed has reached at least 10 km/h since the last time reverse gear was engaged.

The engine stop function is available in modes P and N with the parking brake applied only if mode D or M was engaged beforehand. This is intended to prevent an automatic engine stop after the first "ignition ON" signal.

As the master control unit for the start/stop function, the driver-side SAM 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.

While the engine is running, the driver-side SAM control unit assesses the operating rate of the alternator (G2). The alternator and the driver-side SAM control unit communicate with each other over the powerplant LIN (LIN C1). The driver-side SAM control unit also reads in the data from the battery sensor (B95) about the condition of the on-board electrical system battery and the condition of the on-board electrical system over the battery sensor-LIN (LIN B15). The ME-SFI control unit (N3/10) also sends the signal "Engine running" to the driver-side SAM control unit via the interior CAN (CAN B).

The following signals from the front SAM control unit (N10/10), Supplemental Restraint System control unit (N2/10), the A/C system control unit (N22/1) (with code I01 (Automatic air conditioning)), the instrument cluster (A1), the Electronic Stability Program control unit (N30/4) and the ME-SFI [ME] control unit are read in by the driver-side SAM control unit over the interior CAN:

• Reverse gear, status
• Brake pedal, status
• Clutch pedal switch, status
• Central locking, status
• Seat belt buckle restraint system switch, status
• Humidity and temperature sensor, signal
• Outside temperature, signal
• Vehicle speed, signal
• Coolant temperature, signal

The driver-side SAM control unit evaluates the relevant data, issues the stop enable signal for the engine and sends the signal via the interior CAN to the ME-SFI control unit, which stops the engine.

The ME-SFI control unit then sends the signal "Drivetrain operational" via the interior CAN to the driver-side SAM control unit. This prevents the energy management system from reducing or switching off consumers if the "Engine running" signal is not sent.

All vehicle systems with the exception of the climate control remain active during the automatic engine stop.

During the automatic engine stop, the indicator lamp "ECO start/stop function available" (A1e63) lights up in the instrument cluster.

If not all of the conditions for an automatic engine stop are satisfied, the driver-side SAM control unit sends the information via the interior CAN to the instrument cluster. There the indicator lamp "ECO start/stop function not available" (A1e62) is activated.

Between two automatic engine stops the vehicle must have reached a speed of at least v = 4 km/h or traveled a distance of at least s = 25 m.

Function sequence for engine start 

The function sequence for engine start describes an engine start commanded by the user after an engine stop.

The engine start function is available for vehicles with manual transmission (code 410 (Manual transmission, 5-speed))  , if:

• The clutch is operated when in neutral.

For vehicles with:Automatic transmission (Code 429 (twinamic))  the engine start function is available, if;

• The accelerator pedal is operated.
• Reverse gear is engaged.
• Gear range is in "P", the brake pedal is disengaged and engaged again.
• Gear range is in N with the parking brake applied, and the brake pedal released and depressed again.
• A shift is made to gear ranges "D" or "M".

Pressing the start/stop button in the engine stop state starts the engine and deactivates the automatic start/stop function.

The signals from the driver inputs described above are sent by the corresponding control units via the interior CAN to the driver-side SAM control unit. This evaluates the relevant data and sends the signal "Engine start, request" to the ME-SFI control unit. This then starts the engine and returns the signal "Engine running" to the interior CAN.

If the engine is in the automatic engine stop state and the driver's seat belt buckle or the driver door is opened, the indicator lamp "ECO start/stop function available" flashes and a warning tone sounds for a period of t = 5 s. The engine start function is also disabled. In vehicles with color display, the warning message "When Leaving: Remove Key" appears.

Function sequence for forced engine start 

To ensure that the on-board electrical system stability is also available during engine OFF, the driver-side SAM 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.

Load-intensive consumers can be requested by, for example, the air conditioning system or the driver assistance systems.

As soon as the energy management is no longer able to ensure stability of the on-board electrical system, the driver-side SAM control unit sends the signal "Engine start, request" via the interior CAN to the ME-SFI control unit. 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. In the instrument cluster the indicator lamp "ECO start/stop function not available" lights up.

On the basis of the data from the battery sensor, the driver-side SAM control unit calculates the required alternator target voltage and then launches the alternator regulation (alternator management). For this purpose, the driver-side SAM control unit evaluates the operating rate of the alternator and requests the corresponding specified voltage (excitation voltage). The alternator and the driver-side SAM control unit communicate with each other over the powerplant LIN.

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

Reasons for a forced engine start are:

• The charge level of the battery is below 80 %.
• The vehicle starts to roll (v > 7 km/h).
• Coolant temperature is below 21°C or above 105°C.
• The relative brake pressure drops below -400 mbar.
• The brake pedal is pressed three times or more with the engine off.
• The liftgate is opened.
• The windshield is fogged with moisture (with the air conditioning switched on).
• The interior temperature is outside the set range (climate control).

	Electrical function schematic for automatic engine start/stop		PE54.10-P-2068-97BBA
	Overview of energy management system components		GF54.10-P-9990KJ