Monitoring A Hybrid Drive System, Function - GF08.30-P-5001LFH
Engine 276 in model 222.057/157
Engine 276 in model 222.163
Engine 276 in model 222.173
Engine 651.9 in model 222.004/104
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:
- Functional 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.
Further safety systems such as the deactivation of the hybrid system, temperature monitoring of components of the hybrid system and monitoring of the regenerative brake system are described in more detail in the associated documents.
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. In order to do this, a 12 V/88 Hz interlock signal is looped through all high voltage on-board electrical system assembly parts 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 loopthroughed.
The interlock signal is generated in the battery management system control unit and carried in a series connection across the following component parts (except model 222.163/173):
- High-voltage disconnect device (S7)
- Vehicle interior and engine compartment electrical connector (X18/7)
- Electric refrigerant compressor
- Vehicle interior and engine compartment electrical connector
- Power electronics control unit
- High voltage distributor plate (F34/6)
- Power electronics control unit
- Transmission/frame floor assembly connecting point (X22/4)
- Electric machine
- Transmission/frame floor assembly connecting point
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 carried in a series connection across the following component parts (model 222.163/173):
- High-voltage disconnect device
- Power electronics control unit
- High voltage distributor plate
- Electric machine
- Electric refrigerant compressor
- High voltage PTC heater (N33/5)
- Charger (N83/5)
- DC/DC converter control unit (N83/1) (except 222.173)
The battery management system control unit, the charger and the power electronics control unit are equipped with an evaluation circuit for the interlock signal.
In the rear pre-fuse box (F33) circuit 30 becomes circuit 30c. This is used by the battery management system control unit and the power electronics control unit as a signal line for recognizing a crash event and as a power supply for the contactor (A100s1). If in the event of a crash the supplemental restraint system control unit (N2/10) triggers the detonation fuse in the rear pre-fuse box or if the high-voltage disconnect device opens, 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 (except model 222.163/173)
Interlock circuit (model 222.163)
Interlock circuit (model 222.173)
Function requirements for monitoring the control units functions
- Circuit 50 was switched on at least once since circuit 15 was switched on.
Function sequence for monitoring the control units functions
The first monitoring level (Level 2) contains the comparison of specified/actual values for the torque requested by the driver (accelerator pedal position) and the overall drive torque (sum of all torques produced by the combustion engine and the electric machine). Level 2 in the CDI or 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).
Level 2 in the power electronics control unit further checks whether the drive torque requested by the CDI or ME-SFI [ME] control unit via the CAN network is always greater than the motor torque of the electrical machine calculated on the basis of 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 that checks the basic functions of the first monitoring level in the CDI or ME-SFI [ME] control unit (checking the checker).
| Overview of system components, hybrid drive system | GF08.30-P-9999LFH |