Monitoring A Hybrid Drive System, Function - GF08.30-P-5001GRH
Engine 276.821 in model 166
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 in the ME-SFI [ME] control unit (N3/10), the power electronics control unit (N129/1) and the battery management system control unit (N82/2).
The monitoring concept for the ME-SFI [ME] control unit is sub-divided into the following three levels:
- Functional level (level 1)
- First monitoring level (level 2)
- Second monitoring level (level 3)
While all implemented functions of the hybrid drive system such as torque coordination, energy management, sensor and actor actuation implemented in the ME-SFI [ME] control unit are in the function level, the further levels serve to monitor the system and thus achievement of functional reliability and plausible operation of the vehicle.
Further safety systems such as deactivation of the hybrid drive system, temperature monitoring of components of the hybrid drive system and monitoring of regenerative braking systems are described in more detail in the following 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 battery management system control unit, the charger (N83/5) and power electronics control unit are equipped with an evaluation circuit for the interlock signal.
The Interlock signal is generated in the battery management system control unit and led in a series connection via the following assembly parts:
- Charger
- DC/DC converter control unit (N83/1)
- High-voltage disconnect device (S7)
- High voltage PTC heater (N33/5)
- Electric refrigerant compressor
- Electric machine
- Power electronics control unit
- High voltage distributor plate (F34/6)
- Power electronics control unit
The battery management system control unit, the charger as well as the DC/DC converter control unit and the power electronics control unit have an evaluation circuit for the interlock signal.
In the battery compartment prefuse 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 the supplemental restraint system control unit (N2/10) triggers the detonation fuse in the battery compartment 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 disconnects the high-voltage battery from the high-voltage on-board electrical system.
Shown on model 166.063
Function requirements for monitoring the control units functions
- Circuit 50 was switched on at least once since switching on of circuit 15.
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).
On the ME-SFI [ME] control unit level 2 whether the generated overall drive torque is greater than that requested by the driver via the accelerator pedal sensor (B37). 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 level 2 in the power electronics control unit, it is also checked whether the drive torque requested by the ME-SFI [ME] control unit via the CAN network is always greater than the motor-generated 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 which checks the base function of the first monitoring level in the ME-SFI [ME] control unit (checking the checker).
| Wiring diagram of high-voltage lines and interlock circuit | PE08.00-P-2000-97NBA | ||
| Overview of system components, hybrid drive system | GF08.30-P-9999GRH |