Hybrid drive system, function - GF08.30-P-0001FLM

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 

Interlock circuit

The interlock circuit is used as protection to protect people against inadvertent contact with contacts of the high-voltage components of the high voltage on-board electrical system which are carrying a high voltage.

A 12 V/88Hz interlock signal is looped here through all high voltage on-board electrical system components that are to be dismantled or opened. To do this there is a contact bridge in each removable high voltage plug connection which interrupt the interlock circuit during removal of the high voltage plug 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 is not shown in the following block diagram. The high voltage on-board electrical system is shown schematically with an orange colored line. An overview of the interlock circuit and the high-voltage on-board electrical system can be found in the reference overview:

• Driving, function 

in document

• Monitoring a hybrid drive system, function 

Information about the 12-V energy management of the 12-V on-board electrical system and the 12-V alternator (for a diesel engine) are documented in the function description "energy management function".

Block diagram 

Fig 1: Hybrid Drive System Block Diagram

Courtesy of MERCEDES-BENZ USA

Hybrid drive system - general points 

The hybrid drive includes the control unit for the internal combustion engine, the power electronics control unit (N1291) with the electrical machine (A79/1) and the high voltage on-board electrical system with the battery management system control unit (N822).

The master control unit here is the CDI control unit (N3/9) (for a diesel engine) or the ME-SFI [ME] control unit (N3/10) (for a gasoline engine), which contains the operation strategy, the aggregate coordinator and the energy management and therefore coordinates all energy flows and torques in the hybrid system with the goal of the lowest possible system losses and therefore the lowest fuel consumption.

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

• Power electronics control unit
• Battery management system control unit
• Fully integrated transmission control unit (Y3/8n4)
• Regenerative braking system control system (N30/6) the hybrid system.

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

Hybrid drive system, function 

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

The CDI control unit or the 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. The energy management is responsible for coordination of energy flows and implementation of the operating strategy. 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 electric machines in combination with the internal combustion engine (hybrid driving operation). The electrical machine generates an engine-generated torque for boosting or works as an alternator in regenerative braking.

The power electronics control unit monitors and regulates the electrical machine.

It converts three-phase alternating stress generated by the electrical machine into a 120 V direct voltage and vice versa.

A DC/DC converter is integrated in the power electronics module it designed as a bidirectional DC voltage converter which generates a high and low DC voltage and transfers this between the high voltage on-board electrical system and the 12 V on-board electrical system.

The battery management system control unit monitors the high-voltage battery (A100g1) integrated in the high voltage module which serves as an energy store for the 120 V direct voltage. In order to charge the high-voltage battery, the internal combustion engine drives the electrical machine which then generates an AC voltage as an alternator. This voltage is converted by the power electronics control unit into a 120 V 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 regenerative braking system is a further development of the Electronic Stability Program (ESP) and also, amongst other things, contains the ESP functions and regenerative braking. The recuperative braking allows a braking torque which can be distributed any way one wishes. The regenerative braking system 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 wheel brake) braking torque moment 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 brake torque it is always energy recovery of the brake energy.

Additional information about the subsystems listed here is described in the following documents:

• Common rail diesel injection (CDI), function 
• Regenerative braking system, function 
• Automatic transmission hybrid drive block, function 

CAN network

The ME-SFI [ME] control unit exchanges data via the connected drive train CAN (CAN C) and chassis CAN 1 (CAN E1) with the other control units integrated in the CAN network.

The CDI control unit or the ME-SFI [ME] control unit also acts as the interface (gateway) between the two connected CAN bus systems. The CDI control unit or the ME-SFI [ME] control unit is also connected to the drive train LINE (LINE C1) and exchanges data over it.

Diagnosis

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

The operating conditions of the hybrid system and the active subfunctions of the hybrid system involved are described in the following documents:

• Start hybrid drive system, function 
• High voltage on-board electrical system cooling, function 
• Energy management for hybrid drive system, function 
• Deactivation of hybrid drive system, function 

The functions which are specially active in driving mode and the active subfunctions of the hybrid system involved are described under 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:

• Hybrid drive system test conditions, function 
• Monitoring a hybrid drive system, function 
• Torque coordination for a hybrid drive system, function 
• Automatic engine stop, function 
• Automatic engine start, function 
• Deceleration mode, function 
• Recuperative braking, function