Overview
This document contains information on:
General
Function requirements
Drive only with internal combustion engine
Starting off
BOOST MODE
Load point shifting
Generator mode
Electric mode
General
To generate the drive torque, one of the following is used:
only the internal combustion engine (conventional driving mode),
only the electric machine (electric mode) or
the electric machine in conjunction with the internal combustion engine (hybrid mode) is used.
In conventional driving mode, the electric machine is operated as a generator (generator mode).
In hybrid mode, the torque of the electric machine acts together with the torque of the internal combustion engine. Torque support takes place during start-up and acceleration (boost mode).
In electric mode, the vehicle is powered solely by the electric machine.
Function requirements
Hybrid drive system operational
Selector lever position "D" or "R"
Drive only with internal combustion engine
Unless there is a reason for a different driving state, the conventional driving mode is set.
In conventional driving operation, driving takes place as follows when:
the power required by the driver cannot be provided by the electric machine.
hybrid driving mode is not possible due to an insufficient high-voltage battery charge level.
the engine oil temperature is too low in relation to the outside temperature.
there are errors in the hybrid drive system.
Starting off
Additional function requirements:
No critical fault in the drive system
Vehicle stationary
During driving off the request for torque by the driver is read in by the powertrain control unit. The powertrain control unit calculates the required starting torque and distributes the torque request among the internal combustion engine and the electric machine.
The vehicle is started up on electricity alone if
The torque request from the driver can only be implemented electrically.
no error is reported in the hybrid drive system.
The charge level of the high-voltage battery is too high.
To do this, the powertrain control unit requests an additional motorized torque via the power electronics control unit.
If, in the course of starting up, the torque request as a whole increases, the powertrain control unit starts the internal combustion engine, synchronizes its engine rpm and connects it.
In the case of strong acceleration the electric machine is supported by the internal combustion engine, in particular for acceleration from low engine rpms.
The electrical auxiliary oil pump ensures oil is pumped to the automatic transmission when the combustion engine has been switched off.
BOOST MODE
In boost mode, the electric machine supports the internal combustion engine in order to reach the requested specified torque more quickly or to further amplify the torque beyond the maximum torque achievable by the internal combustion engine. The period and intensity of the boost mode are dependent on the charge level of the high-voltage battery and the position of the accelerator pedal. The powertrain control unit requests an electric machine torque from the power electronics control unit, which then acts on the drive together with the internal combustion engine.
Torque synchronization between the internal combustion engine and the electrical machine is realized in boost mode during driving off via appropriate actuation of the clutch. For this purpose, the powertrain control unit requests actuation of the engine separator clutch. In boost mode in higher vehicle speed ranges the clutch is actuated in such a way that just a regulated zero slip situation is set.
Load point shifting
Additional function requirements:
Charge level of the high-voltage battery < 60 %
No boost mode, no regenerative braking
In hybrid mode, the load point of the internal combustion engines can be shifted by operating the electric machine as a generator and demanding additional torque from the internal combustion engine.
The primary goal of shifting the load points is to keep the internal combustion engine with a good efficiency within a load point range. Load point shifting is also used to heat up the internal combustion engine more quickly by means of additional loading. In this way the CATs are brought up to operating temperature more quickly and the exhaust temperature required for regeneration of the diesel particulate filter is reached (for a diesel engine).
The high-voltage battery's ability to absorb regenerative braking energy decreases as the deviation from the optimum charge level of the high-voltage battery (SOC operating point) increases. This means: if the high-voltage battery is charged at a very high SOC, increased energy losses are incurred in the form of heat. In order to reduce this and to keep space open for potentially arising regenerative braking energy, the high-voltage battery is discharged by the electric machine if a defined SOC value is overshot. The electric machine then works as an engine and delivers torque. The torque delivered by the internal combustion engine is reduced accordingly.
Generator mode
Additional function requirements:
Charge level of the high-voltage battery < 60 %
No boost mode, no regenerative braking or load point shifting
During alternator operation the electric machine, driven by the internal combustion engine, is used as an alternator in order to generate electrical energy.
The electrical energy in the form of a 3-phase AC voltage that is generated in this way is limited, monitored and converted into high voltage direct voltage by the power electronics control unit.
Electric mode
Additional function requirements:
Driver's torque request can be fulfilled by electricity alone.
No fault reported in the hybrid drive system.
Charge level of the high-voltage battery is high enough.
Vehicle speed max. 130 km/h
Transmission oil temperature > 0 °C
Gear range is plausible.
Vacuum in the brake booster is sufficient.
Electronic Stability Program control unit has issued approval.
Hood is closed.
No crash event reported.
12-V on-board electrical system is OK and release has been issued.
Charge level of high-voltage battery is sufficient.
Oil supply to automatic transmission is guaranteed.
Driver door is closed.
Driver seat belt has been fitted.
Interior temperature can be regulated with the current coolant temperature of the internal combustion engine.
A/C has issued approval.
To change from hybrid mode to electric mode, the engine separator clutch is opened and then the combustion engine is switched off.
Electric mode is subdivided into the following operating states:
Electric mode
Crawling
Sailing mode
Electric mode
To meet the driver's torque request, the powertrain control unit requests the required torque from the power electronics control unit.
The power inverter integrated in the power electronics control unit converts the high voltage direct voltage into a 3-phase alternating voltage and supplies this to the electric machine. The power electronics control unit regulates the frequency and amplitude of the alternating stress and therefore directly the generated drive torque dependent on the performance specifications.
Crawling
The crawling that is typical in the automatic transmission if the brake pedal and the accelerator pedal are not pressed is simulated in electric mode via the electric machine. The electric machine is supplied with a low current and acts with the torque produced in this way on the powertrain.
Sailing mode
If the brake pedal and accelerator pedal are not actuated when the vehicle is rolling, the combustion engine is disconnected from the powertrain in Economy (E) drive program up to a speed of 160 km/h by opening the engine separator clutch and is switched off.
Function schematics | |||
Function schematic for driving status control | 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 | |||
Power electronics control unit, basic function | |||
Powertrain control unit, basic function |