Hybrid System

System Outline

This system controls the following modes in order to achieve the most efficient operations to match the driving conditions.

1. Motor Generator Condition
1. Supply of electrical power from the HV battery to motor generator no.2 (Front) provides force to drive the wheels.
2. While the tires are driven by the engine via the planetary gears, motor generator no.1 (Front) activates to supply electricity via the planetary gears to motor generator no.2 (Front) to drive the wheels.
3. When the vehicle is decelerating, kinetic energy from the wheels is recovered into electrical energy and used to recharge the HV battery by motor generator no.2 (Front).

The hybrid vehicle control ECU switches between these modes (1, 2, 1+2, or 3) according to the driving conditions.
However,when the state of charge of the HV battery is low, the HV battery is charged by the engine turning motor generator no.1 (Front).

2. Inverter
- The inverter converts high-voltage direct current of HV battery to three-phase alternating current for driving motor generator no.1 (Front) and motor generator no.2 (Front).
- The activation of the power transistors is controlled by the motor generator control computer. In addition, the inverter transmits necessary information for current control, such as the output amperage or voltage, to the motor generator control computer.
- Along with motor generator no.1 (Front) and motor generator no.2 (Front), the inverter is cooled by the exclusive radiator of the coolant system that is separated from that of the engine.
- In vehicle collision, circuit breaker sensor installed in the inverter outputs collision signal to stop the system.
- Boost converter has been adopted in the inverter, which increases rated voltage output from HV battery of DC 288V, to DC 650V. After increasing voltage, the inverter converts direct current to alternating current.

3. Converter
The power source for auxiliary equipment of the vehicle such as the lights, audio system, and the air conditioning system,as well as the ECUs, is based on a rated voltage of DC 12 V system. Because the HV battery outputs at DC 288 V, the converter is used to transform the voltage from rated voltage of DC 288 V to DC 12 V in order to recharge the auxiliary battery. The converter is installed on the underside of the inverter.

4. HV Battery
- In HIGHLANDER Hybrid Vehicle, the sealed nickel hydride (Ni-MH) battery has been adopted. This HV battery has high power density, lightweight and longevity to match characteristics of hybrid system. Because hybrid system controls charge/discharge to maintain charge/discharge control to maintain SOC (State of charge) at constant level while the vehicle is operating normally, it does not have to rely on the use of external recharges.
- The HV battery, battery voltage sensor, system main relay and the cooling fan are put in a signal case which is placed in the rear seat to make more effective use of vehicle space.
- A service plug that shuts off circuit is provided in the middle of the 30 modules (Rated battery capacity = 288 V). Before servicing any portion of the high-voltage circuits, make sure to remove the service plug.
Please do not READY ON when you remove the service plug. There is a possibility that battery voltage sensor breaks down.
- To ensure the HV battery"s performance, the battery voltage sensor controls the operation of the cooling fan to avoid the head that is generated in the HV battery during charging and discharging.

5. Regenerative System Operation
This system operates the motor as a generator to change the kinetic energy of the vehicle into the electricity when accel pedal is released or foot braking decelerates the vehicle speed, and store the electricity in the battery.

6. E-Four System
E-Four system realizes optimum motive force distribution under various driving conditions by changing from the front-wheel drive which focuses on fuel consumption to the four-wheel drive which focuses on traction performance. The change is brought by driving the front wheels with the motor generator no.2 (Front) and the rear wheels with the motor generator (Rear).