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Hybrid Drive System Test Conditions, Function - GF08.30-P-2005RFH

Engine 274.920 in model 205.047/147/247 

Engine 274.920 in model 205.053/054/253 

Engine 274.920 in model 253.353/953 

Engine 274.920 in model 253.354/954 

Engine 651.921 in model 205.012/212 

Engine 654.920 in model 205.013/213 

IMPORTANT The subfunction "hybrid drive system driving conditions, function" is considered and described from the point of view of the hybrid drive system.

We will not go into more detail here about internal signals and function sequences of the internal combustion engine and the A/T.

Function requirements for hybrid drive system test conditions, general 

Hybrid drive system test conditions, general 

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

For the driving operation with an internal combustion engine the electric machine (A79/1) 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 the electric machine 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 powered by the electric machine.

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

Function sequence for test conditions 

For vehicles with code B53 (External noise sound generator for hybrids and EVs), when the combustion engine is at a standstill, depending on the speed (read in by the left front axle rotational speed sensor (L6/1), right front axle rotational speed sensor (L6/2), left rear axle rotational speed sensor (L6/3) and right rear axle rotational speed sensor (L6/4)) and the accelerator pedal position (read in by the accelerator pedal sensor (B37)) an audio signal is issued between 0 and 30 km/h. At speeds over 30 km/h, the output of the audio signal is deactivated since the rolling and wind noises produced by the vehicle are loud enough to take notice of the vehicle. The audio signal is output via the following component parts:

IMPORTANT The sound generators are also active when drive range "R" is engaged and when the combustion engine is idling due to the legal requirements in the USA.

IMPORTANT The sound generators can be deactivated using the menu in COMAND.

The function sequence is described in the following steps:

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

Additional function requirements for driving off 

Function sequence for driving off 

The vehicle moves according to the torque request of the driver which is read in by the ME-SFI [ME] control unit, initially purely electrically. For a respectively high performance request the internal combustion engine is started, rotational speed-synchronized and then coupled to the traction drive. In the case of strong acceleration the electric machine is supported by the internal combustion engine, in particular for acceleration from low rotational speeds. In the case of driving off from an operating status with the combustion engine, the wet clutch or engine separator clutch is used as a starting device.

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

Driving off purely electrically can occur, if

IMPORTANT If the internal combustion engine is off (e.g. automatic engine stop), the oil supply for the A/T is secured over the electrical auxiliary oil pump (M42).

Function sequence for boost mode 

In boost mode the electric 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 maximum 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 combustion engine and the electric machine is realized in boost mode during driving off via appropriate actuation of the wet clutch or engine separator clutch. To do this, the ME-SFI [ME] control unit requests actuation of the wet clutch or engine separator clutch via the CAN network. In boost mode in higher vehicle speed ranges, the wet clutch or engine separator clutch is actuated in such a way that just a regulated zero slip situation is set. In order to match the torque request from the driver, the ME-SFI [ME] control unit requests in the same way from the power electronics control unit, as for electrical operation, a torque from the electric machine which then operates together with the internal combustion engine on the drive. 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 electric machine.

The power electronics control unit actuates the electric 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 electric 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 operation 

If the transmission mode or the operating mode of electrical drive allows it, the charge level of the high-voltage battery is high enough, the torque request of the driver can be fulfilled purely electrically and no diagnosis or no system error will prevent electrical operation, then this operating condition is adopted. The wet clutch or the engine separator clutch is opened and the combustion engine is switched off by the ME-SFI [ME] control unit if certain prerequisites are fulfilled.

At least all of the following prerequisites must be fulfilled and releases awarded:

The function sequence is subdivided into the following sub-sequences:

Function sequence for electrical driving mode 

In order to meet the request for torque from the driver the ME-SFI [ME] control unit or the CDI control unit makes a request to the power electronics control unit for the required immediate torque from the electric machine according to the load request.

The power electronics control unit actuates electric machine the appropriately on the basis of signals "tolerable discharge voltage" and "tolerable discharge current", reported by ME-SFI [ME] control unit or the CDI control unit. To do this the ME-SFI [ME] control unit or the CDI control unit requests from the power electronics control unit the previously calculated motorized torque from the electric machine. This is provided with energy from the high-voltage battery over the power electronics control unit and acts 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 3-phase AC voltage.

The ME-SFI [ME] control unit or the CDI control unit makes the request via the CAN network to the fully integrated transmission control unit for actuation of the wet clutch or engine separator clutch in order to disconnect the combustion engine from the drive. After appropriate feedback via the opened wet clutch or engine separator clutch, the ME-SFI [ME] control unit switches the combustion engine off. If during the automatic engine stop a release is retracted or a prerequisite is no longer fulfilled, the internal combustion engine will automatically be started without any defined action on the part of the driver.

Function sequence for creeping 

The creeping that is typical of automatic transmission is simulated via the electric machine or via the combustion engine and slipping of the wet clutch or engine separator clutch if the brake pedal and the accelerator pedal are not actuated. For creeping in electrical mode the electric machine is supplied with a low current and operates directly on the drivetrain with acts with the torque that is generated in this way. If the high-voltage battery has a low state of charge, for example, creeping is realized via the combustion engine and slipping of the wet clutch or engine separator clutch.

Additional function requirements for alternator operation 

Function sequence for cruising mode 

If the brake pedal and accelerator pedal are not actuated when the vehicle is rolling, the combustion engine is disconnected from the drive in the Economy (E) drive program up to a speed of < 160 km/h by opening the wet clutch or engine separator clutch and is switched off.

For a slightly actuated accelerator pedal, the electric machine supports the drive for an adequately high charge level of the high-voltage battery 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 CAN network. This actuates according to the request from the electric machine.

Function sequence for alternator operation 

During alternator operation the electric machine, driven by the internal combustion engine, is used as an alternator in order to generate electrical energy.

In order to do this, the rotational energy of the crankshaft is taken up by the rotor of the electric machine. Rotation of the rotor causes an AC voltage to be induced in the three stator windings. 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.

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 assembly parts.

Additional function requirements for load point shifting 

Function sequence for load point shifting 

The possibility of take up of recuperation energy by the high-voltage battery increases with increasing deviation from the optimal charge level of the high-voltage battery (SOC operating point). This means, 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 combustion engine by the electric machine upon exceeding a defined 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 objective is to keep the shift in the load point within the load point range with good efficiency as far as possible. The load point shift is also used to put additional load on the internal combustion engine. 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).

  Electrical function schematic for vehicle statuses of the hybrid drive system   PE08.30-P-2069-97FBH 
  Overview of system components, hybrid drive system   GF08.30-P-9999RFH 
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