Overview
This document contains information on:
General
Function level
Monitoring of the control unit functions (torque)
Hardware-implemented monitoring function of the control units monitoring
Interlock circuit
General
Monitoring in the powertrain control unit is divided into the following levels:
function level (Level 1)
First monitoring level (level 2, monitoring of the function level)
Second monitoring level (level 3, hardware monitoring)
The battery management system control unit takes on the monitoring of the interlock circuit.
Function level
All functions of the electric drive implemented in the powertrain control unit are contained in the monitoring on the function level.
Monitoring of the control unit functions (torque)
The first monitoring level (level 2) contains the specified-actual comparison of the specified drive torque (calculated from the accelerator pedal position, recuperation level, and information of the ESP®) and actual drive torque.
In the powertrain control unit, level 2 checks whether the specified torque of the function level is located within the scope of the information presented by the accelerator pedal position, recuperation level, and ESP®. If this is not the case, the specified torque of the function level is limited accordingly before it is requested by the power electronics control unit.
In level 2, in the power electronics control unit, the plausibility of the torque requested by the powertrain control unit is checked using the information of the ESP® and the torque is limited if necessary. Apart from that, the set actual drive torque of the electric machine is calculated. The power electronics control unit checks whether the plausibility value of the specified drive torque is always larger than the calculated actual drive torque. In addition, the direction of the torque and compliance with a permanently set maximum torque are checked. In the event of deviations, the electric machine is passively switched by the power electronics control unit, i.e. it does not generate any torque.
In addition to the torque, further variables are monitored at level 2, e.g. the recuperation request, the drive range, or the park pawl.
Hardware-implemented monitoring function of the control units monitoring
The second monitoring level (level 3) is based on hardware monitoring. For this purpose, level 3 carries out checks, which ensure the correct version of the function software and level 2. In the event of an error, the electric machine is passively switched by the power electronics control unit.
Apart from that, a self-sufficient control monitor also exists, which checks the basic functions of the first monitoring level in the powertrain control unit.
Interlock circuit
The interlock circuit provides protection against accidentally touching the high voltage components. An interlock voltage signal is looped through all high-voltage on-board electrical system component 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. Furthermore, the high-voltage on-board electrical system in selector lever position "D" is also switched off when opening the hood. If the ignition is switched off and interlock circuit has an open circuit, the vehicle can no longer be driven.