Battery System, Hybrid Drive: Description and Operation

FUNCTION DIAGNOSIS

HYBRID BATTERY SYSTEM

System Diagram









System Description

GENERAL
- The hybrid vehicle control ECU detects the amount of effort applied to the accelerator pedal in accordance with the signals provided by the accelerator pedal position sensor. The hybrid vehicle control ECU receives signals from the speed sensor (resolver) in the MG1 and MG2, and detects the shift position signal from the shift position sensor. The hybrid vehicle control ECU determines the driving conditions of the vehicle in accordance with these pieces of information, and optimally controls the motive forces of MG1, MG2, and the engine. Furthermore, the hybrid vehicle control ECU optimally controls the output and torque of these motive forces in order to realize lower fuel consumption and cleaner exhaust emissions.
- The hybrid vehicle control ECU calculates the engine motive force based on the calculated target motive force, and by taking the SOC and the temperature of the HV battery module into consideration. The value obtained by subtracting the engine motive force from the target motive force is the MG2 motive force.
- The hybrid vehicle control ECU sends the target engine motive force signal and the target engine speed signal to the ECM through CAN communication line. The ECM optimally controls the electric throttle control actuator and sends the actual engine speed signal to the hybrid vehicle control ECU. Furthermore, the hybrid vehicle control ECU appropriately operates MG1 and MG2 in order to realize the required MG2 motive force.

NOTE:
- Inverter water pump is also called water pump with motor and bracket assembly.
- Generator is also called MG1 or motor generator No.1.
- Traction motor is also called MG2 or motor generator No.2 drive motor.
- Inverter assembly is also called inverter with converter assembly inverter.
- Hybrid vehicle converter (DC/DC converter) is also just called DC/DC converter.






SYSTEM MONITORING CONTROL
- The hybrid vehicle control ECU constantly monitors the SOC (state of charge) of the HV battery. When the SOC is below the lower level, the hybrid vehicle control ECU increases the power output of the engine to operate MG1, which charges the HV battery. When the engine is stopped, MG1 operates to start the engine, then the engine operates MG1 to charge the HV battery.
- If the SOC is low, or the temperature of the HV battery module, MG1 or MG2 is higher than the specified value, the hybrid vehicle control ECU restricts the motive force applied to the drive wheels until it is restored to the normal value.

SHUT DOWN CONTROL
The MG1 and MG2 are shut down when the shift position is in the N position. This is because MG1 and MG2 must be stopped electrically as a means of shutting down the motive force, since MG2 is mechanically joined to the front wheels.

BATTERY SMART UNIT CONTROL
- The battery smart unit monitors the HV battery condition signals (voltage, current and temperature), which are needed to determine the charging or discharging values that are calculated by the hybrid vehicle control ECU and transmits them to the hybrid vehicle control ECU via serial communication.
- A leakage detection circuit is provided in the battery smart unit in order to detect any leakage from the HV battery.
- The battery smart unit monitors the voltage of the cooling fan, which is needed by the hybrid vehicle control ECU to effect cooling fan control, and transmit it to the hybrid vehicle control ECU via serial communication.






SMR (SYSTEM MAIN RELAY) CONTROL
1. General
The SMR is a relay that connects and disconnects the power source of the high-voltage circuit upon receiving a command from the hybrid vehicle control ECU.

A total of three relays are used: one (SMRB) at the positive side, and two (SMRP and SMRG) at the negative side. One (SMRP) of the relays at the negative side is a semiconductor relay, which is integrated in the DC/DC converter. The other two are contact point type relays, which are mounted on the junction box in the HV battery module.






2. Power is ON
The hybrid vehicle control ECU turns the SMRB ON. After that, it turns the SMRP ON.
After the hybrid vehicle control ECU has turned the SMRG ON, it turns the SMRP OFF.
As the controlled current is initially allowed to pass through a resistor in this manner, the contact point in the circuit is protected from damage that could be caused by a rush current.






3. Power is OFF
- First, the hybrid vehicle control ECU turns the SMRG OFF. After it has determined whether the contact points of the SMRG are stuck, it turns the SMRB OFF.
- Afterwards, the hybrid vehicle control ECU turns the SMRP ON in order to determine whether the contact points of the SMRB are stuck. Then, it turns the SMRP OFF.
- If the hybrid vehicle control ECU detects that the contact points are stuck, it illuminates the master warning light and indicates "CHECK HYBRID SYSTEM" on the multi-information display, and stores a DTC (Diagnostic Trouble Code) in memory.






SOC CONTROL
- The hybrid vehicle control ECU calculates the SOC (state of charge) of the HV battery by monitoring its charging and discharging amperages, in order to effect condition control.
- While the vehicle is in motion, the HV battery undergoes repetitive charging/discharging cycles, as it becomes discharged by the MG2 during acceleration and charged by the regenerative brake during deceleration. The hybrid vehicle control ECU calculates the SOC based on charging/discharging levels detected by the current sensor. The hybrid vehicle control ECU performs the charging/discharging control based on the calculated value in order to steady the SOC at its target level anytime.






POWER CABLE
The power cable is a high-voltage, high-amperage cable that connects the HV battery module with the inverter, the inverter with MG1 and MG2, and the inverter with the electric inverter compressor. The power cable starts at the connector of the junction block of the HV battery, which is located behind the rear seat.
It passes under the floor panel, along the side of the floor reinforcement, and connects to the inverter in the engine compartment. The power cable is shielded in order to reduce electromagnetic interference.

For identification purposes, the high-voltage wiring harness and connectors are color-coded orange to distinguish them from those of the ordinary low-voltage wiring.