Hybrid Drive System, Function - GF08.30-P-0001RFH

Engine 274.920 in model 205.047/147/247, 253.954 

Engine 274.920 in model 205.053/253 

Engine 274.920 in model 253.354 

Engine 651.921 in model 205.012/212 

Engine 654.920 in model 205.013/213 

Interlock circuit

The interlock circuit is used as contact protection to protect people against inadvertent contact with high-voltage components. The interlock is an anticipatory contact which opens a little before the high-voltage connection when opening a high-voltage connection. In this way timely discharging of the high voltage intermediate circuit is achieved by the control units of the high-voltage components.

In order to do this, a 12 V/88 Hz interlock signal is looped through all assembly parts of the high voltage on-board electrical system that can be removed or opened. To do this there is an electrical bridge in each removable high-voltage connection which interrupts the interlock circuit during removal of the high-voltage connection. The interlock circuit is also led switched in a series over the 12 V control units plug connection of the high-voltage components.

The interlock circuit and the high voltage on-board electrical system are not shown in the following block diagram. An overview of the interlock circuit and the high voltage on-board electrical system can be found in the driving operation reference overview  and additional information can be found in the document (Hybrid drive system function monitoring.) 

We will not go into more detail here about internal signals and function sequences of the internal combustion engine, the A/T, the RBS and the 12 V on-board electrical system.

Courtesy of MERCEDES-BENZ USA

Block diagram (except model 205.047/147/247, model 253.954/354) 

Courtesy of MERCEDES-BENZ USA

Block diagram (model 205.047/147/247, model 253.954/354) 

Model 205.047/147/247

DC/DC converter

A DC/DC converter is integrated in the power electronics control unit, which converts the high voltage direct voltage (primary voltage) into 12 V direct voltage (secondary voltage) and vice versa and transfers these between the high voltage on-board electrical system and the 12 V onboard electrical system.

Model 253.354/954

DC/DC converter control unit

The DC/DC converter control unit is installed in the vehicle as a separate component. The DC/DC converter control converts high-voltage direct voltage (primary voltage) into 12-V direct voltage (secondary voltage) and transfers these between the high voltage on-board electrical system and the 12-V on-board electrical system.

Hybrid drive system - general points 

The hybrid drive system includes the control of the internal combustion engine, the power electronics control unit with the electrical machine and the high voltage on-board electrical system with the battery management system control unit, the charger (model 205.047/147/247, 253.954/354) and the DC/DC converter control unit (model 253.954/354).

The master control unit is the CDI control unit (for a diesel engine) or the ME-SFI [ME] control unit (for a gasoline engine) which includes the major assembly coordinator and thus also all torques in the hybrid drive system with the goal of obtaining the least possible system losses and therefore the least possible fuel consumption.

The energy management which takes on coordination of energy flows and implementation of the energy management, is integrated in the powertrain control unit.

The CDI control unit or the ME-SFI [ME] control unit in a CAN network creates with the components

• Drivetrain control unit
• DC/DC converter control unit (model 253.954/354)
• Charger (model 205.047/147/247, model 253.954/354)
• Power electronics control unit
• Battery management system control unit
• Fully integrated transmission control, control unit
• Electronic Stability Program control unit makes the hybrid drive system.

The following table provides an overview of the vehicle model and major assembly overviews:

• Start hybrid drive system, function 
• Stationary charging function (model 205.047/147/247, model 253.954/354) 
• Energy management for hybrid drive system, function 
• High-voltage system cooling, function 
• Deactivation of hybrid drive system, function 
• The functions which are specially active in driving mode and the active subfunctions of the hybrid drive system involved are listed in the following document:
  • Driving, function 

The functions which are specially active in driving mode and the active subfunctions of the hybrid drive system involved subdivide into the following documents:

• Deceleration mode, function 
• Vehicle conditions of the HYBRID system function 
• Automatic engine stop, function 
• Automatic engine start, function 
• Monitoring the HYBRID system function 
• Torque coordination for a hybrid drive system, function 
• Recuperative braking, function 

Hybrid drive system, function 

The components of the hybrid drive system fulfill a number if functions including:

The CDI control unit or ME-SFI [ME] control unit is responsible for controlling the internal combustion engine, computation of the specified axle torque through prioritization of the external torque requests and their implementation. In order to generate the drive torque one either just uses the internal combustion engine (conventional driving operation), only the electrical machine (electrical driving operation) or the electrical machines in combination with the internal combustion engine (hybrid driving operation). The electrical machine generates an engine-generated torque for a boost effect or operates as an alternator in regenerative braking.

The powertrain control unit contains the energy management, which coordinates the energy flows and implements the energy management. The power electronics control unit monitors and regulates the electrical machine. This converts 3-phase AC voltage generated by the electrical machine into high voltage direct voltage and vice versa.

The DC/DC converter control unit (model 253.954/354) enables energy to be exchanged between the high voltage on-board electrical system and the 12-V on-board electrical system, by transforming the high voltage direct voltage (primary voltage) into 12-V direct voltage (secondary voltage).

The charger (model 205.047/147/247, model 253.954/354) converts the AC voltage of an external voltage source (e.g. charging station) into direct voltage for charging the high-voltage battery. The high voltage direct voltage is used to charge the high-voltage battery (model 205.047/147/247, model 253.954/354).

The battery management system control unit monitors the high-voltage battery integrated into the high-voltage battery module, which serves as an energy store for the high voltage direct voltage. In order to charge the high-voltage battery, the internal combustion engine drives electrical machine which then generates an AC voltage as an alternator. This voltage is then converted by the power electronics control unit into a high voltage direct voltage. In order to retrieve the kinetic energy or to generate the requested braking torque, the electrical machine is actuated as an alternator and converts kinetic energy into electrical energy which is then stored.

The fully integrated transmission control unit takes on monitoring and controlling of the automatic transmission.

The Electronic Stability Program (ESP), amongst other things, contains the functions of the ESP® and the recuperative braking. The regenerative braking is the braking torque which can be divided up over the software. The Electronic Stability Program control unit divides the overall braking torque moment requested by the driver according to the driving condition into a regenerative (to be implemented by the drivetrain) part and an hydraulic (to be implemented over the service brake) braking torque part and requests the regenerative part from the CDI control unit or the ME-SFI [ME] control unit. In the case of a portion of the regenerative braking torque it is always energy recovery of the brake energy.

CAN network

The CDI control unit or ME-SFI [ME] control unit exchanges data with other control units that are integrated in the CAN network via the connected engine CAN and drive train CAN. The CDI control unit or the ME-SFI [ME] control unit also acts as the interface (gateway) between the two CAN bus systems. The CDI control unit or the ME-SFI [ME] control unit is also connected to the drivetrain LIN or powertrain LIN, which is used to exchange data.

Diagnosis

For diagnostic purposes, the fault codes from the hybrid drive system can be read off and deleted with Mercedes' Xentry Diagnostics, and specific diagnostic functions initiated.

The operating conditions of the hybrid drive system and the active partial functions of the hybrid drive system are described in the following documents: