Overview
This document contains information on:
General
Function requirements
Automatic start of the combustion engine
General
An automatic engine start is initiated if the vehicle needs energy for the traction which cannot be delivered purely electrically or if changes in system conditions requires starting of the internal combustion engine.
The start of the combustion engine is requested by the combustion engine control unit.
Depending on the model, a separate starter is available in addition to the electric machine.
A combustion engine start takes place depending on the input of the major assembly coordinator interface in the combustion engine control unit via:
The starter (e.g. in electric mode)
The electric machine (in the event of vehicle stillstand or for vehicles without starter)
The starter and the electric machine together (in electric mode).
For vehicles with starter, the following applies:
The start of the combustion engine can take place only via the electric machine, if the vehicle is stationary and the charge level of the high-voltage battery is high enough.
During electric mode, if the engine separator clutch is open, the combustion engine is started first via the starter up to a certain engine speed. If this starting speed is reached then the internal combustion engine is subsequently up to idle speed over the drive through closing the clutch.
For vehicles without starter, the following applies:
The start of the combustion engine takes place after closing the engine separator clutch via the electric machine.
Function requirements
Hybrid system operational
Engine stops after an automatic engine stop (electrical operation)
System diagnosis complete and fault-free
No crash event in this driving cycle
Engine hood closed
Automatic start of the combustion engine
When the combustion engine is stationary, the combustion engine control unit assesses, on an ongoing basis, whether the function requirements for the automatic engine stop are continuing to be fulfilled.
If one of the following listed releases is retracted or a condition is no longer fulfilled, the internal combustion engine is started.
Starting of the internal combustion engine is initiated if
Vehicle speed > 160 km/h
Transmission oil temperature < 0 °C
The vacuum in the brake booster is not adequate
Enable canceled by ESP®
12-V energy management has canceled the enable
Charge level of the high-voltage battery under the limit value
Oil supply for the automatic transmission via the electric auxiliary oil pump not safeguarded
driver identified as absent
interior temperature cannot be regulated with the current coolant temperature of the internal combustion engine
Control of the climate control has canceled the enable signal
An automatic engine start can occur for every engaged gear range. If the vehicle is brought to a standstill after electric operation and the driver door is opened, the driver is reminded about the continuing driving readiness of the vehicle. For an engaged gear range "P" or "N" the internal combustion engine is started as a reminder. For an engaged drive range of "D" or "R," a indication occurs in the multifunction display.
For the automatic engine start during the vehicle stillstand, the required motorized torque of the electric machine is calculated by the combustion engine control unit. In order to prevent an automatic engine stop and, for an opened hood, an automatic engine start, the status of the hood is read in by the combustion engine control unit.
The combustion engine control unit requests actuation of the engine separator clutch from the fully integrated transmission control unit to connect the combustion engine with the automatic transmission.
After receiving the corresponding feedback via the closed engine separator clutch, the combustion engine control unit requests actuation of the electric machine from the power electronics control unit to start the combustion engine.
The combustion engine control unit detects the end of the starting procedure via the engine speed or, in the event of a torque-led start, via a differential torque assessment between the motorized torque generated by the electric machine and the torque of the combustion engine.
Function schematics | |||
Function schematic for hybrid system engine start | Model 167 with code ME05 (Hybrid drive 85 kW-94 kW variant (incl. plug-in))Model 213 as of model year 2021 with code ME05 (Hybrid drive 85 kW-94 kW variant (incl. plug-in))Model 213 as of model year 2021 with code ME08 (Hybrid drive 75-84 kW VARIANT (INCLUDING PLUGIN)) | ||
Model 177, 247 with code ME08 (Hybrid drive 75-84 kW VARIANT (INCLUDING PLUGIN)) | |||
Control units | |||
Combustion engine control unit, basic function |