Hybrid system monitoring, basic function

Overview:

This document contains information on:

 General

 Function level

 Monitoring the control units functions

 Hardware-implemented monitoring function of the control units monitoring

 Interlock circuit

General

Monitoring within the powertrain control unit and power electronics is divided into the following levels:

 function level (Level 1)

 first monitoring level (Level 2)

 second monitoring level (Level 3)

The interlock monitoring occurs using the interlock circuit via the battery management system control unit.

Function level

All functions of the hybrid system implemented in the powertrain control unit are contained in the monitoring on the function level. These are, for example, torque coordination, energy management, and sensor and actuator control.

Monitoring the control units functions

The first monitoring level (level 2) contains the specified-actual comparison of the driver's request torque (accelerator pedal position) and overall drive torque (sum of all torques from the combustion engine and electric machine).

In the powertrain control unit, level 2 checks whether the generated overall drive torque is larger than that requested by the driver via the accelerator pedal sensor. If this is the case, it is assumed that there is a fault in the powertrain control unit and the system changes to the limp-home function of the combustion engine (rpm limitation 1500 rpm).

In the power electronics control unit in level 2, an additional check is performed as to whether the drive torque requested the powertrain control unit is always larger than the motor-generated torque of the electric machine calculated from the currents and position angle of the rotor. The electrical machine is switched to passive by the power electronics control unit if this is the case.

Hardware-implemented monitoring function 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 functions of the first monitoring level in the powertrain control unit (checking the checker).

Interlock circuit

The interlock provides protection against accidental touching of live parts of 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 (interlock circuit). 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 only once 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 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.

 In the pyrofuse, circuit 30t 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. If the supplemental restraint system control unit triggers the fuse in the pyrofuse in the event of a crash or the high-voltage disconnect device is opened, the circuit 30c signal line is interrupted and the contactor in the high-voltage battery interrupts the connection of the high-voltage battery to the high-voltage on-board electrical system.