Automatic Start, Basic Function - GF07.10-P-1052A

Engine all (CAR) 

Overview 

This document contains information on:

• General
• Function requirements
• Function
  • Start with integrated separating module
  • Start with voltage dip limiter

General 

The engine starts automatically when the accelerator pedal is actuated or the brake pedal is released.

Function requirements 

• Ignition ON (circuit 15)
• Engine management ON (circuit 87 M)
• Outside temperature between -10 and 40 °C
• On-board electrical system battery temperature 0 to 60 ?
• System diagnosis complete and fault-free

Function 

The automatic starting procedure takes place when the engine is in automatic stop and the ignition is still switched on.

An automatic starting procedure takes place under the following conditions:

• The clutch pedal is actuated (manual transmission)
• The brake pedal is released (when the HOLD function is not active and the transmission position is D or N (automatic or dual-clutch transmission))
• The accelerator pedal is actuated (automatic or dual-clutch transmission)
• The drive program is changed (automatic or dual-clutch transmission)
• Vehicle starts to roll
• The temperature in the vehicle interior goes outside the selected range
• Air conditioning switched on

Start with integrated separating module 

Hybrid vehicles with an integrated separating module are not equipped with a voltage dip limiter or support battery for the starting procedure. During the starting procedure, the integrated separating module decouples the starter battery and starter from the on-board electrical system. During the starting procedure, the 12 V on-board electrical system is supplied with power via the DC/DC converter. When the starting procedure is complete and the combustion engine is operating, the integrated separating module opens and the on-board electrical system is reconnected to the starter battery.

Start with voltage dip limiter 

A voltage dip limiter on the positive pole of the on-board electrical system battery delays the voltage drop during the automatic starting procedure. The starting procedure ends as soon as the engine reaches a rotational speed of 400-700 rpm.

The voltage dip limiter is an electrically switchable series resistor used to reduce the high power consumption of the starter when the engine is cranked. The voltage dip limiter is connected to the starter circuit 50 relay via circuit 87. When the engine is started, voltage is supplied to the voltage dip limiter. This helps it recognize the starting procedure and activate the series resistor. If the on-board electrical system voltage drops too much due to the high power consumption of the starter, the voltage dip limiter switches the series resistor off.

If the voltage drop at engine start is too large (U < 11 V), an automatic engine stop is not permitted for one minute to allow the ECO start/stop function auxiliary battery to recharge. The ECO start/stop function auxiliary battery is switched in only if the on-board electrical system voltage is high enough (U > 13 V). It is disconnected again when the alternator management is active or the on-board electrical system is severely overloaded.

The external engine start/stop unit operates with starter-assisted direct starting. After the engine stops, the crankshaft angle in the rest position is stored in the combustion engine control unit using the crankshaft angle sensor. When the engine starts, synchronization of the fuel injection system and the ignition system that is otherwise required is no longer necessary due to the stored crankshaft angle.