Starting and Charging: Description and Operation

GF54.10-P-1070FL Engine Start/stop Automatic Function
- with CODE (B03) ECO start/stop function

Function requirements, general
^ Engine is running and is at operating temperature (Coolant temperature :
- on engine 271 = T > 60 °C < 115 °C
- on engine 651 = T > 15 °C < 130 °C)

^ Engine hood closed
^ One-time overspeeding of v > 15 km/h in forward travel
^ SD [system diagnosis] completed
^ Outside temperature T = -10 to 40 °C
^ Battery temperature T = 0 to 60 °C
^ Air conditioning regulated

Engine start/stop automatic, general
When the vehicle is stationary the task of the engine/start stop automatic is to switch off the engine automatically and to start the engine again as soon as the driver would like to start off. Switching off the engine during standstill periods of the vehicle reduces the fuel consumption and thus carbon dioxide emission. The conventional switching off and starting the engine with the transmitter key (A8/1) or via the Start-stop-KEYLESS-GO button (S2/3) (with code (889) Keyless Go) continues to be possible.

A detailed description of the engine start/stop system function is contained in the function description of the gasoline injection and ingition system Motor-Electronics (ME) or in the function description of the CDI [common rail diesel Injection] (CDI).

The master control unit of the engine automatic start/stop system is the ME-SFI control unit (N3/10) or the CDI control unit (N3/9), which acquires and evaluates all the influencing factors Through the use of the additional battery for ECO start/stop function (G1/13) with a capacity of 12 Ah the starting voltage dip is supported while the engine is being started.
The additional battery for ECO start/stop function takes over the voltage supply of all active consumers in the process, while the on-board electrical system battery (G1) is decoupled from the on-board electrical system.
Active comfort functions are not switched off consequently.

Immediately after the cold start of the engine the ME-SFI control unit or the CDI control unit carries out a system diagnosis and evaluates the function capability of the engine automatic start/stop system. The front SAM control unit with fuse and relay module (N10/1) also checks the function of all relevant components for isolating the on-board electrical system battery and connecting the additional battery for ECO start/stop function.

The additional battery for ECO start/stop function is connected by the relay for additional battery for ECO start/stop function (K114). On vehicles with manual transmission it is designed as a mechanical relay and in vehicles with A/T as an electronic relay The decoupling of the on-board electrical system from the on- board electrical system battery takes place on vehicles with manual transmission by the on-board electrical system decoupling relay (K19/7) and in vehicles with A/T by the diode for ECO start/stop function (V19).

The engine automatic start/stop system is activated by pressing the ECO start/stop function button (N72/1s50) in the upper control panel (N72/1). The status of the ECO start/stop function button is read-in by the UCP control unit, and forwarded over the instrument panel LIN (LIN 1) to the front SAM control unit. The front SAM control unit transmits the status of the ECO start/stop function button via the chassis CAN (CAN E) to the ME-SFI control unit. When the function requirements are met the readiness for operation of the engine automatic start/stop system is displayed to the driver by the "ECO" symbol in the multifunction display (A1p13) of the IC (A1).

The function engine start/stop automatic is subdivided into the following partial functions:
^ Function sequence for engine stop
^ Function sequence of automatic engine start
^ Function sequence for determine condition of additional battery for ECO start/stop function
^ Function sequence for charge additional battery for ECO start/stop function

Additional function requirements of Engine stop
^ Stop enable granted by the ME-SFI control unit or CDI control unit

Function sequence for engine stop
As the master control unit for the automatic engine start/stop system, the ME-SFI checks the following parameters for stop enable:
- No voltage dip (U > 11 V) at the additional battery for ECO start/stop function since the last automatic engine start
- Coolant temperature in specified value range
- Oil temperature in specified value range
- engine rpm in specified value range
- Transmission selector lever position "D" or "N" (with transmission 722)
- Gearshift lever in neutral (on transmission 716.6)
- Engine automatic start/stop system activated via the ECO start/ stop function button
- Vehicle speed V ≥ 8 km/h
- Data from the on-board electrical system and energy management provided by the SAM rear SAM control unit with fuse and relay module (N10/2):
- Outside temperature in specified value range
- Condition of on-board electrical system battery OK
- Condition of additional battery for ECO start/stop function OK
- On-board electrical system condition (no consumption-intensive requirements (I > 100 A))

- Status of driver recognition:
- Driver door closed and driver seat belt being worn

- Status of A/C:
- Interior temperature regulated
- No request of functions "Defrost windshield" or "Maximum cooling output"
- No fogging of windshield
- No high solar radiation

- Engine hood closed
- No crash event detected
- Brake pedal depressed or "Hold"-function active
- Adequate vacuum present in brake booster
- No control intervention function from BAS and distance control system
- No large steering wheel angle

The ME-SFI control unit or the CDI control unit evaluates all parameters and then grants the stop enable accordingly. Based on this the engine is switched off.

During the vehicle standstill the brake pedal must stay depressed or the "Hold"-function be active. With the active blower automatic of the A/C the blower output is reduced. With warm ambient temperatures the system changes into air recirculation mode independent of the adjusted specified temperature.

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

Function sequence of automatic engine start
The engine is started automatically when the accelerator pedal is pressed (A/T) or the clutch pedal (manual transmission) is depressed. During the starting process the on-board electrical system battery is disconnected from the on-board electrical system and the starting voltage dip otherwise tangible for the vehicle occupants prevented.
The ME-SFI control unit or the CDI control unit evaluates all relevant variables and grants the start enable. This is read in by the front SAM control unit via a direct line. The front SAM control unit then actuates the decoupling relay for the on-board electrical system (manual transmission) or the diode for ECO start/stop function (A/T) in the front prefuse box (F32) and the additional battery relay for the ECO start/stop function on the additional battery for ECO start/stop function. This connects the additional battery for ECO start/stop function to the on-board electrical system.
Shortly after that the decoupling relay for the on-board electrical system (manual transmission) or the diode for the ECO start/stop function (A/T) disconnects the on-board electrical system battery from the on-board electrical system for the duration of the starting process.

The energy requirement of the on-board electrical system is now solely covered by the additional battery for ECO start/stop function. This measure prevents the starting voltage dip which can be experienced by the vehicle occupants.
The on-board electrical system battery now serves alone the provision of the energy required for the starting process of the engine.
As soon as the ME-SFI control unit or the CDI control unit detects an engine speed of n = 400 to 700 rpm, it ends the starting process and transmits a corresponding signal to the rear SAM control unit.
Based on this the rear SAM control unit switches on the on-board electrical system decoupling relay and the additional battery for the ECO start/stop function. The decoupling relay for on-board electrical system (manual transmission) or 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 on-board electrical system. The energy requirement of the on-board electrical system is now covered solely again by the on-board electrical system battery.

Component Identification:

Function sequence for determine condition of additional battery for ECO start/stop function
In order to generate information about the availability of electrical power from the additional battery for ECO start/stop function, a simple battery state recognition is integrated in the front SAM control unit. This is carried out immediately after the engine has been started. If the engine is switched off while the carrying out of the battery state recognition, the front SAM control unit aborts the battery state recognition and rejects the results from the previous measurement.
In addition to battery state recognition, the voltage of the additional battery for ECO start/stop function in the engine start/stop automatic mode is tested each time the engine starts. The battery state recognition can be started by means of a diagnosis tester. If the additional battery for ECO start/stop function is deep discharged, this indicates an internal short circuit or if a short circuit in the positive line of the additional battery for ECO start/stop function is determined, the additional battery relay for ECO start/stop function is not operated.

In order to establish this, the voltage of the additional battery for ECO start/stop function is compared with an internal value. A corresponding fault message is shown in the instrument cluster's multifunction display. The rear SAM control unit transmits the data required for this to the IC via the interior CAN.

Function sequence for charge additional battery for ECO start/ stop function
The charging strategy of the additional battery for ECO start/stop function must take into account two criteria:
- The ECO start/stop function additional battery must always be sufficiently charged
- The number of actuations of the additional battery relay for ECO start/stop function must be minimized as far as possible.

If the open circuit voltage (U > 12.5 V) of the additional battery for ECO start/stop function is too low, the generator management is deactivated so that the additional battery for ECO start/stop function can be charged.

If the voltage dip (U < 11 V) is too large when the engine starts, an engine stop will be deactivated for t = 5 min in order to recharge the additional battery for ECO start/stop function. The additional battery for ECO start/stop function is only started if no generator management is active and the on-board electrical system voltage (U > 13 V) is high enough.

It is cleared again when the generator management is active or the on-board electrical system is severely overloaded.