Hybrid drive system test conditions, function - GF08.30-P-2005FLM

ENGINE 276.952 in MODEL 212.095 as of model year 2014 

ENGINE 651.924 in MODEL 212.098/298 as of model year 2014 

The subfunction "hybrid drive system driving conditions, function" is considered and described from the point of view of the hybrid system. Internal signals from the internal combustion engine which are read in during the driving conditions are described in the following documents:

• Synchronization of fuel injection and firing order function 
• Torque coordination, function 

Function requirements for hybrid drive system test conditions, general

• Hybrid system "READY" (green)
• Selector lever position "D" or "R"

Hybrid drive system test conditions, general 

Differentiation of the driving operation is made between internal combustion engine, hybrid driving mode and electric driving mode (cruising mode, maneuvering).

For the driving operation with an internal combustion engine the electrical machine is mostly run as an alternator (alternator mode)

According to the request and charge level of the high-voltage battery (A100g1), in hybrid driving mode the torque from electrical machines (A79/1) operates together (supportively) with the torque of the internal combustion engine. The support occurs during moving off and acceleration (boost mode).

In electrical driving mode driving of the vehicle is purely electrical by the electrical machine.

The CDI control unit (N3/9) (for a diesel engine) or the ME-SFI [ME] control unit (N3/10) (for a gasoline engine) reads in the following signals in hybrid driving mode:

• Accelerator pedal sensor (B37)
• Engine load request from the driver
• Accelerator pedal operation fast or slow (when acceleration)
• Regenerative braking system control unit (N30/6), wheel speed over chassis CAN 1 (CAN E1)
• Wheel speed, signal
• Service brake status
• Lowering torque, request
• Battery management system control unit (N82/2) via hybrid CAN (CAN L)
• Voltage of high-voltage battery
• Temperature of high-voltage battery
• Video and radar sensor system control unit (N62/2) (for code (233) DISTRONIC PLUS code (237) Active Blind Spot Assist or code (238) Active Lane Keeping Assist), request for change of torque via the chassis FlexRay (Flex E) and chassis CAN 1
• Power electronics control unit (N129/1)
• Status of electrical machine over the hybrid CAN
• Torque of electrical machine
• Rotational speed of electrical machine
• Charging voltage/current, signal via the hybrid CAN
• Fully integrated transmission control unit (Y3/8n4) via the drive train CAN (CAN C)
• Wet clutch status
• Gear range, status

Function sequence for test conditions 

The function sequence is described in the following steps:

• Function sequence for drive with the internal combustion engine 
• Function sequence for driving off 
• Function sequence for boosting 
• Function sequence for electrical driving mode 
• Function sequence for alternator operation 
• Function sequence for load point shifting 

Function sequence for drive with the internal combustion engine 

The drive with the internal combustion engine represents the standard driving mode.

Driving occurs in standard driving mode if:

• The output desired by the driver cannot be delivered by the electrical machine.
• The hybrid driving mode is not possible due to a low charge level of the high-voltage battery.
• The engine oil temperature is too low in comparison with the outside temperature.
• Error the in hybrid system reported.

Additional function requirements for driving off 

• No critical fault in the drive system
• Vehicle at rest

Function sequence for driving off 

During driving off the request for torque by the driver is read in by the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or ME-SFI [ME] control unit calculates and distributes the required starting torque to the internal combustion engine and the electrical machine. To do this the CDI control unit or ME-SFI [ME] control unit requests an additional motorized torque via the power electronics control unit.

The electrical machine is supplied over the power electronics control unit with energy from the high-voltage battery.

Driving off purely electrically can occur, if:

• The driver's requested torque can be delivered purely electrically
• No error reported in the hybrid system
• The charge level of the high-voltage battery is adequately high

If the internal combustion engine is off (e.g. automatic engine stop), the oil supply for the AT is secured over the electrical transmission oil pump (M42).

Additional information on the automatic engine start/stop and the oil supply for the automatic transmission is available in the following documents:

• Automatic engine start, function 
• Automatic engine stop, function 
• Oil supply for automatic transmission, function 

Function sequence for boost mode 

In boost mode the electrical machine supports the internal combustion engine in order to reach the requested specified torque as quickly as possible or to further amplify the drive torque to amplify the achieved internal combustion engine torque. The period and intensity of the boost mode are hereby dependent on the charge level of the high-voltage battery and the position of the accelerator pedal. Torque synchronization between the internal combustion engine and electrical machine is realized over respective actuation of the wet clutch. To do this the CDI control unit or the ME-SFI [ME] control unit requests actuation of the wet clutch via the drive train CAN.

Additional information concerning actuation of the wet clutch is described in the following document:

• Wet clutch, function 

In order to meet the request for torque from the driver the CDI control unit or the ME-SFI [ME] control unit makes a request to the power electronics control unit for the maximum available torque from the electrical machine. The power electronics control unit actuates the electrical machine appropriately based on the signals tolerable discharge voltage/current reported by the CDI control unit or the ME-SFI [ME] control unit. To do this the CDI control unit or the ME-SFI [ME] control unit requests from the power electronics control unit the previously calculated motorized torque from the electrical machine. This is provided with energy from the high-voltage battery over the power electronics control unit and works together with the internal combustion engine on the drive.

Function sequence for electrical driving mode 

The hybrid system allows purely electrical driving for low specified axle torque-requests and speeds <35 km/h. This applies both for forwards and reverse travel.

The function sequence is subdivided into the following transmission modes:

• Function sequence for electrical driving mode 
• Function sequence for creeping 
• Function sequence for cruising mode 

Function sequence for electrical driving mode 

For a low torque requested by the driver and an adequately high charge level of the high-voltage battery, the CDI control unit or the ME-SFI [ME] control unit requests from a power electronics control unit a specified torque from the electrical machine. The power electronics control unit actuates the electrical machine as a motor and acts in this way on the drive. To do this the high-voltage battery supplies the power electronics control unit with a direct voltage, which is converted into a three-phase AC voltage. In order to disconnect the internal combustion engine from the drive, the CDI control unit or the ME-SFI [ME] control unit requests the respective actuation of the wet clutch via the drive train CAN.

Function sequence for creeping 

The creeping typical for the A/T is simulated electrically over the electrical machine or over the internal combustion engine and the slip of the wet clutch if the brake and accelerator pedal is not actuated.

Creeping electrically: 

For electrical creeping the electrical machine is supplied with a low current and acts with the torque produced in this way directly on the drivetrain.

Creeping with the internal combustion engine: 

For a situation such as a low charge level of the high-voltage battery the creeping is realized over the internal combustion engine and the slip of the wet clutch.

Function sequence for cruising mode 

If the brake and accelerator pedal are not actuated for a rolling vehicle, the internal combustion engine is disconnected from the engine in the transmission mode Economy (E) up to a speed < 160 km/h through opening the wet clutch and switched off. For an adequately high charge level of the high-voltage battery and a slightly actuated accelerator pedal, the electrical machine supports the drive for in order to counteract the falling vehicle speed. To do this the CDI control unit or the ME-SFI [ME] control unit requests an engine-generated torque from the power electronics control unit via the hybrid CAN. This actuates according to the request from the electrical machine.

Additional function requirements for alternator operation

• SOC (State of Charge) <60%
• No boosting, no regenerative braking or load point shifting

Function sequence for alternator operation 

During alternator operation the electrical machine, driven by the internal combustion engine, is used as an alternator in order to generate electrical energy. To do this the rotational energy of the crankshaft is taken up by the rotor of the electrical machine. Rotation of the rotor causes an AC voltage to be induced in the three stator windings. The electrical energy so generated is limited in the form of a three-phase AC voltage by the power electronics control unit, monitored and converted into the high voltage direct voltage. The power electronics control unit uses the energy generated to supply the high voltage on-board electrical system, the electrical A/C compressor (A9/5) and the 12 V on-board electrical system and its components.

Additional function requirements for load point shifting

• SOC >70%
• No boost effect

Function sequence for load point shifting 

The efficiency of the high-voltage battery reduces with increasing deviation from the SOC operating point. If the high-voltage battery is charged or discharged for a low or very high SOC value, increased energy losses are incurred in the form of heat. In order to reduce this and to keep space open for potentially arising regenerative energy, the high-voltage battery is discharged with the support of the internal combustion engine by the electrical machine for exceeding of the SOC value. In this way the load point of the internal combustion engine is shifted. That means that the torque of the internal combustion engine is reduced by the CDI control unit or the ME-SFI [ME] control unit. The goal is to shift the load points as much as possible within the load point range while maintaining a good efficiency. Furthermore, the load point shifting is used in order to load the internal combustion engine more strongly in order to bring the CAT up to operating temperature or to the exhaust temperature required to achieve regeneration of the diesel particulate filter.