Describe the purpose and the different modes of operation of the system main relays.

What will be an ideal response?


The HV ECU controls the operation of the system main relay (SMR) to connect and disconnect the power source of the high-voltage system. Initially SMR1 and SMR3 are turned on to energize the circuit for the HV battery to provide the required current for the motor generator to start the engine. Then SMR2 is energized and SMR1 is turned off to make the current from the generator flow through a resistor, thus controlling the amount of current flow. SMR2 is turned on and SMR1 is turned off to allow free flow of current in the circuit. During shutdown, SMR2 is turned off first, then SMR3. This provides a means for the HV ECU to verify that the relays have been properly turned off.

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