Starting and Charging: Description and Operation

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

Function requirements, general
^ Engine is running and it 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
^ A/C 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 of the engine during stillstand periods of the vehicle reduces the fuel consumption and therefore the carbon dioxide emissions.
The conventional switching off and starting the engine with the transmitter key (A8/1) or via the KEYLESS-GO start-stop button (S2/3) (with code (889) Keyless-Go) continues to be possible.

A detailed description of the engine start/stop 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 (CDI) [Common Rail Diesel Injection.

The master control unit of the engine start/stop-automatic is the ME-SFI control unit (N3/10) (with gasoline engine) or CDI control unit (N3/9) (with diesel engine) which records and evaluates all influencing factors. By the use of the additional battery for ECO start/stop function (G1/13) with a capacity of I = 12 Ah the starting voltage dip is prevented while the engine is starting. The additional battery for ECO start/stop function takes over the power supply of all 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 CDI control unit carries out a system diagnosis [SD] and evaluates the functional capability of the engine start/stop automatic.

In addition the front SAM control unit with fuse and relay module (N10/1) checks the function of all affected 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 additional battery relay 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 on-board electrical system is decoupled from the on-board electrical system battery by the decoupling relay (K19/7) on vehicles with manual transmission and in vehicles with A/T by the diode for the ECO start/stop function (V19).

The engine start/stop-automatic is activated by pressing the ECO start/stop function button (N72/1s50) in the UCP [upper control panel]control unit (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 or CDI control unit. When the function requirements are met, the readiness for operation of the engine start/stop-automatic 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 requirement for engine stop
^ Stop enable granted by ME-SFI control unit or CDI control unit

Function sequence for engine stop
As master control unit of the engine start/stop-automatic the ME-SFI control unit or CDI control unit check 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 (with transmission 711, 716)
- Engine start/stop-automatic 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 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 consumer-intensive requests (I > 100 A))

- Status of driver detection
- 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 levels of solar radiation

- Engine hood closed
- No crash event detected
- Brake pedal depressed or "Hold" function active
- Sufficient vacuum available in brake booster
- No control intervention function from BAS system 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 approval accordingly. The engine is switched off as a result of this.

While the vehicle is at a standstill the brake pedal must remain pressed or the "Hold" function be active. The blower output is reduced when the automatic blower system of the A/C is active. In high ambient temperatures the system changes into air circulation mode depending on the specified temperature adjusted. After an automatic engine stop a maximum of three automatic starts are 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 (A/ T) or clutch pedal (manual transmission) is pressed. During the starting process the on-board electrical system battery is disconnected from the on-board electrical system and the starting voltage dip otherwise experienced by the vehicle occupants is prevented.
For this the ME-SFI control unit or CDI control unit CDI read in the signals of the accelerator pedal sensor (B37) (A/T) or of the clutch pedal switch (S40/3) (manual transmission) via a direct line. The incoming signals are evaluated accordingly.
When start enable is granted, the front SAM control unit actuates the additional battery relay for the ECO start/stop function at the additional battery for the ECO start/stop function, in order to connect the additional battery for ECO start/stop function to the on-board electrical system. 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) in order to disconnect the on- board electrical system battery from the on-board electrical system.

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 CDI control unit detects an engine rpm of n = 400 to 700 rpm, it stops the starting process and transmits a corresponding signal 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 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 found, the additional battery relay for ECO start/ stop function (manual transmission) or the diode for start/stop function (A/T) is not actuated.
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 via the interior CAN (CAN B) to the IC.

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 is started, an engine stop is 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 connected when 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.