Monitoring A Hybrid Drive System, Function - GF08.30-P-5001RFH
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
Function requirements for monitoring a hybrid drive system, general points
- Control units for the hybrid drive system activated over the Wake-up Function
Monitoring a hybrid drive system - general points
Monitors and limits the system monitoring as part of driving safety during acceleration the drive torque of the vehicle on the basis of the driver specification by means of the accelerator pedal position.
Function sequence for monitoring a hybrid drive system
The whole monitoring concept is integrated into the CDI control unit (N3/9) (for a diesel engine) or the ME-SFI [ME] control unit (N3/10) (for a gasoline engine), in the power electronics control unit (N129/1) as well as in the battery management system control unit (N82/2).
The monitoring concept for the CDI control unit or the ME-SFI [ME] control unit is subdivided into the following three levels:
- function level (Level 1)
- first monitoring level (Level 2)
- second monitoring level (Level 3)
While the function level contains all the functions implemented in the CDI or ME-SFI [ME] control unit for the hybrid drive system such as, e.g. torque coordination, energy management, sensor and actuator actuation, the remaining levels are used to monitor the system, and thereby to assure the vehicle's functional reliability and plausible characteristics.
Additional safety systems such as, e.g hybrid drive system deactivation and the temperature monitoring of the hybrid drive system components are described in greater detail in the following documents, for more information refer to the appropriate service information:
- Energy management for hybrid drive system, function
- Deactivation of hybrid drive system, function
- High voltage on-board electrical system cooling, function
- Automatic engine stop, function
- Automatic engine start, function
The regenerative braking system monitoring is described in a separate scope.
These two monitoring levels are described in more detail below:
- Function sequence for the interlock circuit
- Function sequence for monitoring the control units functions
- Function sequence for hardware-implemented monitoring of the control units monitoring
Function sequence for the interlock circuit
The interlock circuit is used as contact protection to protect people against inadvertent contact with high-voltage components. For this purpose, a 12 V/88 Hz interlock signal is looped through all high voltage on-board electrical system components 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.
When detaching a control units plug connection the interlock circuit is interrupted via the contacts interlock input and output.
A discontinuity of the interlock circuit while driving does not lead to switching off of the high voltage on-board electrical system. The high voltage on-board electrical system is only switched off if the selector lever position "N" or "P" is engaged for > 3 s and the vehicle speed is < 5 km/h. Furthermore the high voltage on-board electrical system is also switched off in the selector lever position "D" for opening of the engine hood. After switching off the ignition the vehicle cannot be started again if there is a fault in the interlock circuit. For an existing fault in the interlock circuit the vehicle standstill functions (ignition "OFF") are interrupted and the high voltage on-board electrical system deactivated. This means that every access to the high-voltage on-board electrical system leads to an interruption of the interlock circuit and thus to the deactivation of the high-voltage on-board electrical system under the above-mentioned conditions and to prevent the activation of the high-voltage on-board electrical system.
The error statuses can also be determined through evaluation of signals from the interlock circuit in the active high-voltage components (e.g. discontinuity, short circuit). In the other components (electrical A/C compressor (A9/5), electrical machine (A79/1)), the interlock circuit is loop-throughed.
The interlock signal is generated in the battery management system control unit and led in a series connection over the following components (except model 205.047/147/247):
- Electric refrigerant compressor
- Power electronics control unit
- High-voltage disconnect device (S7)
- Electric machine
The battery management system control unit is fitted with an evaluation circuit for the interlock signal.
The interlock signal is generated in the battery management system control unit and guided in a series circuit via the following component parts (model 205.047/147/247, 253.354/954):
- Charger (N83/5)
- High voltage PTC heater (N33/5)
- Electric refrigerant compressor
- High-voltage disconnect device
- Electric machine
- Power electronics control unit
- High voltage distributor plate (F34/6)
- Power electronics control unit
- DC/DC converter control unit (N83/1) (model 253.354/954)
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 on-board electrical system.
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.
The battery management system control unit is fitted with an evaluation circuit for the interlock signal.
In the pyrofuse (F63), circuit 30 becomes circuit 30c. This serves the battery management system control unit and power electronics control unit as a signal line to recognize a crash event as well as the contactor as a power supply. If the supplemental restraint system control unit (N2/10) triggers the detonation fuse in the rear prefuse box or the high-voltage disconnect device is opened as a result of a crash, the circuit 30c signal line is interrupted and the contactor in the high-voltage battery (A100g1) disconnects the high-voltage battery from the high-voltage on-board electrical system.
Interlock circuit shown on model 205.012/212
Interlock circuit shown on model 205.047/147/247
Electrical fuses in high-voltage battery
There are electrical fuses that can be replaced in the high-voltage battery (electrical fuse 750 and electrical fuse 751). These are placed under a removable cover (with interlock contact breaker point (3)), and located in the electric circuit behind the contactor.
This way, the electrical fuses are not energized when the power disconnect operates correctly.
Shown: high-voltage battery module with opened fuse panel (model 205.047/147/247)
Interlock circuit shown on model 253
Electrical fuses in high-voltage battery
There are replaceable fuses in the high-voltage battery (electrical fuse 750, electrical fuse 751, and electrical fuse 752). These are placed under a removable cover (with interlock contact breaker point), and located in the electric circuit behind the contactor.
This way, the electrical fuses are not energized when the power disconnect operates correctly.
Shown on high-voltage battery module with open fuse panel (model 253)
Function requirements for monitoring the control units functions
- Circuit 50 was set at least once since circuit 15 ON.
Function sequence for monitoring the control units functions
The first monitoring level (Level 2) contains the nominal-actual comparison from the driver's request torque (accelerator pedal position) and the overall drive torque (sum of all torques from the internal combustion engine and the electrical machine).
Level 2 in the CDI control unit or the ME-SFI [ME] control unit checks whether the generated overall drive torque is greater than that requested by the driver via the accelerator pedal sensor (B37). The CDI control unit or the ME-SFI [ME] control unit assumes there is a fault if this is the case and the system changes over into the limp-home function of the internal combustion engine (RPM limitation 1500 RPM).
In the power electronics control unit in level 2 a check is also performed as to whether the drive torque requested by the CDI control unit or ME-SFI [ME] control unit via CAN network is always greater than the motor-generated torque of the electrical machine calculated on the basis of the currents and the position angle of the rotor. The electrical machine is switched to passive by the power electronics control unit if this is the case.
Function sequence for hardware-implemented monitoring of the control units monitoring
The second monitoring level (Level 3) is based on self-contained hardware monitoring. It consists of a control monitor which checks the basic function of the first monitoring level in the CDI control unit or the ME-SFI [ME] control unit (checking the checker).
| Wiring diagram of high-voltage lines and interlock circuit | Engine 651.921 in model 205.012/212 | PE08.00-P-2000-97FBB | |
| Wiring diagram of high-voltage lines and interlock circuit | Engine 274.920 in model 205.047/147/247 | PE08.00-P-2000-97FBA | |
| Wiring diagram of high-voltage lines and interlock circuit | Engine 274.920 in model 253.354/954 | PE08.00-P-2000-97FBC | |
| Deactivation of hybrid drive system, function | GF08.30-P-1004RFH | ||
| Energy management for hybrid drive system, function | GF08.30-P-1005RFH | ||
| Automatic engine stop, function | GF08.30-P-3001RFH | ||
| Automatic engine start, function | GF08.30-P-3002RFH | ||
| High-voltage system cooling, function | GF20.00-P-2220RFH | ||
| Overview of system components, hybrid drive system | GF08.30-P-9999RFH |