Hybrid system engine stop, basic function

Overview

This document contains information on:

 General

 Function requirements

 Automatic stop of the combustion engine

General

The combustion engine control unit initiates an automatic engine stop if the required drive torque can be applied purely electrically or if the system optimization requires the combustion engine to be cut out.

 In the event of an automatic engine stop, circuit 15 is not switched off.

For an automatic engine stop, releases of external systems are required, e.g.:

 High-voltage on-board electrical system

 12 V on-board electrical system

 vehicle climate control

 Regenerative braking system

Function requirements

 Hybrid system operational

 Engine runs

 System diagnosis complete and fault-free

 No crash event in this driving cycle

 Engine hood closed

 Vehicle speed< 160 km/h

 Transmission oil temperature > 0 °C

 If the automatic start/stop intervals exceed an established number in a certain time, the automatic engine stop is suppressed for a certain period of time.

Automatic stop of the combustion engine

When the combustion engine is running, the combustion engine control unit assesses, on an ongoing basis, whether the function requirements for an automatic engine stop are fulfilled.

The electric auxiliary oil pump secures the hydraulic system's oil supply in the automatic transmission when the internal combustion engine is switched off.

The combustion engine is switched off by the combustion engine control unit if certain internal prerequisites concerning the combustion engine and all the following prerequisites are fulfilled:

 gear range plausible

 Adequate vacuum in the brake booster

 Enable issued by ESP®

 the condition of the 12-V on-board electrical system is OK and release has been issued

 Charge level of high-voltage battery is sufficient

 oil supply to A/T secured

 Driver door closed

 Driver seat belt applied

 interior temperature can be regulated with the current coolant temperature of the internal combustion engine

 Control of the climate control has issued enable signal

The combustion engine control unit requests actuation of the engine separator clutch from the fully integrated transmission control unit to disconnect the combustion engine from the drive. After the corresponding feedback via the opened engine separator clutch, the combustion engine control unit switches off the combustion engine.

If a release is retracted after a successful automatic engine stop or a prerequisite is no longer fulfilled, the combustion engine is automatically started.