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Technology File - Safety Technology

Hybrid Vehicle

Introducing the technologies used in Toyota’s hybrid vehicles.

  • AEngine (Atkinson-cycle)
  • BHybrid Transaxle
  • CPower Control Unit
  • DBattery (Nickel-metal Hydride/Lithium-ion)
  • EElectrical 4WD System (E-Four)

HV

Toyota Hybrid System (THS II)

<Fuel Economy> Global Top Level1

Leveraging the strengths of both engines and motors for overwhelming fuel efficiency and powerful performance.

There are several types of Hybrid Systems. Toyota’s THS II (Toyota Hybrid System II) is a Series/Parallel Hybrid System. This system uses both ……

Toyota Hybrid System (THS II)

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Engine (Atkinson-cycle)

<Maximum Thermal Efficiency> Global Top Level1

High thermal efficiency engine produces world-class fuel efficiency.

Toyota’s hybrid vehicles have the Atkinson-cycle engine, which offers superb thermal efficiency. They feature a wide lineup of Atkinson-cycle engines,……

Engine (Atkinson-cycle)

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Hybrid Transaxle

Global First1

Low loss, compact design for greater fuel and space efficiency.

This unit is composed of a motor, generator, and power split device. The new (2015) Prius has relocated the reduction gear mechanism (the reductio ……

Hybrid Transaxle

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Power Control Unit

The brain of the hybrid vehicle, expertly controlling electricity.

The power control unit converts AC/DC power and appropriately adjusts the electrical voltage. Hybrid vehicles powered by motors are equipped with a ……

Power Control Unit

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Regenerative Braking

Collecting otherwise discarded energy and reusing it as driving energy.

The regenerative braking system reuses vehicle deceleration energy. When brakes are applied or the accelerator is eased off, the rotational energy ……

Regenerative Braking

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Battery (Nickel-metal Hydride/Lithium-ion)

Toyota First1Column

Better fuel efficiency, greater controllability, expanded luggage space.
These are all made possible by battery advances.

The cooling system compactness and optimized internal device layout of the main relay and other components in batteries eliminate dead space ……

Battery (nickel-metal hydride/lithium-ion)

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Electrical 4WD System (E-Four)

Toyota First1

The newly developed, high performance, compact HV4WD for compact hybrid vehicles.

Unlike a mechanical 4WD system, the electrical 4WD system (E-Four) does not link the front and rear wheels with a propeller shaft, instead them ……

Electrical 4WD system (E-Four)

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  • Toyota Hybrid System (THS II)

    Global Top Level

    Toyota Hybrid System (THS II)

    Leveraging the strengths of both engines and motors for overwhelming fuel efficiency and powerful performance.

    <Fuel Economy> Global Top Level1Toyota Hybrid System (THS II)

    Leveraging the strengths of both engines and motors for overwhelming fuel efficiency and powerful performance.

    There are several types of Hybrid Systems. Toyota’s THS II (Toyota Hybrid System II) is a Series/Parallel Hybrid System. This system uses both a motor and an engine to drive the wheels, and can also generate electricity during motor operation. It runs on the motor, which offers excellent low speed torque, or the engine, with its high speed performance, or a combination of the two, depending on driving conditions, for powerful, high efficiency driving at all times. It also reuses the excess energy produced during standard driving and low speed driving in electrical generation, improving fuel efficiency. The entire system used in the new (2015) Prius was designed to offer the ultimate in high efficiency, compact size, light weight, and low loss, achieving one of the world’s highest levels of fuel efficiency1.

    1. As of December 2015. Gasoline-powered passenger vehicles (excluding plug-in hybrid vehicle). According to Toyota Motor Corporation.
    Toyota Hybrid System (THS II)
    Basic structure

    The system is composed of the electric motor, the engine, the battery, the generator, the power split device and the power control unit (inverter/boost converter/DC/DC converter). The power split device transfers part of the power produced by the engine to drive the wheels, and the rest to the generator to either provide electric power for the motors or to recharge the battery.

    Basic structure
    Other hybrid systems

    In the Series Hybrid System, the electric power produced from the engine drive is fed to the electric motor that drives the wheels. The engine is not used for vehicle drive. The basic components of the system are the electric motor, the engine, the battery, the generator, and the inverter. The low output engine is quasi-steadily operated to drive the generator, which is connected in series to the motor, hence the name Series Hybrid System.
    In the Parallel Hybrid System, the wheels are driven by both the engine and the electric motor. The basic components of the system are the electric motor, the engine, the battery, the inverter, and the transmission. Battery power is used to drive the motor, which is used as a generator, so, unlike the Toyota THS II, it is not capable of driving with the motor while generating electricity.

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  • Engine (Atkinson-cycle)

    Global Top Level

    Engine (Atkinson-cycle)

    High thermal efficiency engine produces world-class fuel efficiency.

    <Maximum Thermal Efficiency> Global Top Level1Engine (Atkinson-cycle)

    High thermal efficiency engine produces world-class fuel efficiency.

    Toyota’s hybrid vehicles have the Atkinson-cycle engine, which offers superb thermal efficiency. They feature a wide lineup of Atkinson-cycle engines, from 1.5-liter engines to 3.5-liter engines. Among these, the 1.8-liter 2ZR-FXE engine used in the newest Prius (2015) has greatly improved thermal efficiency thanks to its increased cooled exhaust gas recirculation (EGR)2 flow, redesigned intake port shape, and cool air duct. It also uses the Atkinson cycle’s ability to increase the engine’s basic compression ratio, which determines the thermal efficiency, resulting in a compression ratio of 13.0 despite using regular gasoline.

    1. As of December 2015. Internal measurement value.
    2. EGR: Exhaust Gas Recirculation

    The same engine is used in plug-in hybrid vehicles.

    Cooled EGR

    The flow volume of the exhaust gas is cooled by the electric EGR valve and is channeled into the intake manifold, decreasing pumping loss and engine cooling loss in the engine. In the new (2015) Prius the ERG distribution channels in the intake manifold have been redesigned to increase and equalize the amount of the recirculated EGR distributed into each cylinder, resulting in more efficient combustion.

    Intake port shape optimization

    The intake port provides cylinders with the air they need for combustion. In the new (2015) Prius, the shape of the intake port has been optimized to produce a more direct flow of air into the cylinder, strengthening its tumble flow3. At the same time, the piston head shape has been changed to maintain the same tumble flow strength while increasing combustion speed.

    1. Vertical swirl of air that promotes air-fuel mixture. The flow in the direction of the piston’s stroke is called tumble flow.
    Cool air duct

    Thermal efficiency is increased by efficiently drawing dense, cold air into the engine. The new (2015) Prius uses a compact, lower positioned air cleaner to support vehicle bodies with lower hoods. It also has a dedicated intake opening for drawing in large amounts of air when driving at high speeds.

    Engine (Atkinson-cycle)
    1. The piston is depressed while the throttle is open, eliminating wasteful resistance.
    2. Valve delayed closure
      Excess intake is adjusted by delaying the timing of valve closure.
    3. Compression stroke/expansion stroke
      Highly efficient system which enables a longer expansion stroke than compression stroke.
    * Conceptual image.

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  • Hybrid Transaxle

    Global First

    Hybrid Transaxle

    Low loss, compact design for greater fuel and space efficiency.

    Global First1Hybrid Transaxle

    Low loss, compact design for greater fuel and space efficiency.

    This unit is composed of a motor, generator, and power split device. The new (2015) Prius has relocated the reduction gear mechanism (the reduction gear mechanism which amplifies the motor’s torque) to parallel gears as the drive motor to reduce drive loss by approximately 20%2. Dual-axis structure was used for the motors to reduce the total transaxle length by roughly 12%2. Furthermore, the power control unit is installed on top of the transaxle, making the Hybrid System more compact and lightweight.

    1. As of December 2015. According to Toyota Motor Corporation.
    2. Internal measurement value.
    Hybrid Transaxle

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  • Motor

    Toyota First

    Motor

    A more highly evolved motor for even greater driving enjoyment.

    Toyota First1Motor

    A more highly evolved motor for even greater driving enjoyment.

    The system uses a synchronous AC motor together with the engine for drive power. This synchronous AC motor efficiently generates a large amount of torque from low to high speed operation. The motor speed and torque are freely controllable. This produces powerful, smooth driving. The new (2015) Prius offers greater motor speeds and uses segmented coil distributed winding for the stator that generates the rotation force, producing greater output in a more compact, lightweight motor.

    1. As of February 2017.

    The same motor is used in plug-in hybrid vehicles.

    Redesigned motor shape for greater compact vehicle driving.

    One of the attractions of hybrid vehicles is their powerful acceleration. The high output motors used to achieve this tend to be large, hobbling compact vehicles. The new (2015) Prius uses a higher RPM motor to maintain high output while reducing its size by 20% or more2. This increases the freedom with which it can be placed in the vehicle, and will result in further changes in future compact vehicle driving.

    1. Internal measurement value.
    Motor

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  • Generator

    Generator

    A compact generator that provides the motor with a large amount of electrical power.

    Generator

    A compact generator that provides the motor with a large amount of electrical power.

    The generator uses a synchronous AC motor with high speed axial rotation. This generator supplies a large amount of electrical power when driving at low speeds. This enables the high output motor and engine to be combined for greater acceleration at low and medium speeds. The new (2015) Prius uses centralized winding of coils for a more compact, lightweight design.

    The same generator is used in plug-in hybrid vehicles.

    Generator

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  • Power Split Device

    Power Split Device

    Economically splitting power produced by the gas/petrol engine between the drive train and the generator.

    Power Split Device

    Economically splitting power produced by the gas/petrol engine between the drive train and the generator.

    The power splitting device distributes the power produced by the gas/petrol engine to the drive train and to the generator. To divide the power efficiently, it uses a planetary gear consisting of a ring gear, pinion gears, a sun gear and a planetary carrier.

    The same power split device is used in plug-in hybrid vehicles.

    Drive transfer loss is a waste of power.

    The rotating axle of the planetary carrier is directly connected to the gas/petrol engine and rotates the perimeter ring gear and the sun gear inside via the pinion gears. The rotating axle of the ring gear is directly connected to the electric motors, and thus transfers the driving power to the wheels. The axle of the sun gear is directly connected to the generator and converts the power produced by the gas/petrol engine into electric energy. These optimized arrangements and gear ratios reduce drive transfer loss.

    Power Split Device

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  • Reduction Gear

    Reduction Gear

    Drawing a large amount of torque from a compact motor.

    Reduction Gear

    Drawing a large amount of torque from a compact motor.

    The reduction gear is designed to reduce the high rpm of the motors so that the power produced can be transferred to the wheels, amplifying the torque and generating greater driving power. This torque amplification effect, coupled with the higher revving capability of the motors, combines to provide seamless acceleration at will.

    The same reduction gear is used in plug-in hybrid vehicles.

    Reduction Gear

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  • Power Control Unit

    Power Control Unit

    The brain of the hybrid vehicle, expertly controlling electricity.

    Power Control Unit

    The brain of the hybrid vehicle, expertly controlling electricity.

    The power control unit converts AC/DC power and appropriately adjusts the electrical voltage. Hybrid vehicles powered by motors are equipped with a power control unit that consists of an inverter, a boost converter, and a DC/DC converter. Low loss elements are used to achieve superb loss reductions.
    The new (2015) Prius features a more compact power control unit, making it possible to mount it directly above the transaxle and place the auxiliary battery in the engine room, creating a more spacious interior.

    The same power control unit is used in plug-in hybrid vehicles.

    Inverter

    Converting electricity and supplying it from the battery to the motor.

    Motors cannot be operated by connecting them directly to the battery. The inverter converts DC supplied by the battery to AC to turn the electric motors and to use in the generator. Conversely, it converts AC generated by the electric motors and the generator into DC to recharge the battery. Dual side cooling, which directly cools power elements, is featured in the new (2015) Prius, improving cooling efficiency and enabling inverter downsizing and weight reduction.

    Boost converter

    Controlling voltage and boosting low voltages.

    The boost converter controls the voltages of the motor and generator. It steplessly increases the normal roughly 200 V DC supply voltage to a maximum of 650 V DC as required. This means more power can be generated from a small current to bring out high performance from the high output motors, enhancing overall power control unit efficiency.

    DC/DC converter

    Steps down voltage precisely, enabling electricity to be used for purposes other than driving.

    The DC/DC converter steps down the supply voltage from the high voltage battery. It steps down the roughly 200 V DC supply voltage from the battery to 12 V DC, to be used by engine ancillary systems which assist with motor operation and electronic devices such as headlights.

    Power Control Unit

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  • Regenerative Braking

    Regenerative Braking

    Collecting otherwise discarded energy and reusing it as driving energy.

    Regenerative Braking

    Collecting otherwise discarded energy and reusing it as driving energy.

    The regenerative braking system reuses vehicle deceleration energy. When brakes are applied or the accelerator is eased off, the rotational energy of the wheels is used to turn a motor, which functions as a generator. The system coordinates regenerative braking and the braking operation of the hydraulic brakes so that kinetic energy, which is normally discarded as friction heat when braking, is converted to electrical energy and collected by the battery for later reuse in normal driving mode. Typically, driving in city traffic entails a cycle of acceleration followed by deceleration. The energy recovery ratio under these driving conditions can therefore be quite high. To take advantage of this situation, the system proactively uses regenerative braking when running the car in the low speed range.

    The same regenerative braking is used in plug-in hybrid vehicles.

    Regenerative Braking
    Mechanism conceptual diagram

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  • Battery (Nickel-metal Hydride/Lithium-ion)

    Toyota FirstColumn

    Battery (Nickel-metal Hydride/Lithium-ion)

    Better fuel efficiency, greater controllability, expanded luggage space. These are all made possible by battery advances.

    Toyota First1Battery (Nickel-metal Hydride/Lithium-ion)

    Better fuel efficiency, greater controllability, expanded luggage space.
    These are all made possible by battery advances.

    The cooling system compactness and optimized internal device layout of the main relay and other components in batteries eliminate dead space and make it possible for the batteries to be installed under the rear seats. Not only do they offer high fuel efficiency, they also contribute to reducing vehicle weight, greater stability and controllability by lowering vehicle center of gravity, and provide greater luggage space. The new (2015) Prius lineup includes both nickel-metal hydride and lithium-ion batteries. Nickel-metal hydride batteries use newly developed electrode material and battery case design for dramatically increased charge performance. Lithium-ion batteries have dramatically increased output performance due to their use of newly developed electrode materials and reduced cell resistance. Both nickel-metal hydride and lithium-ion batteries charge at a constant level at all times by monitoring and computing the cumulative amount of discharge under acceleration, and recharging by regenerative braking or with surplus power under normal running conditions. They also eliminate the need for external charging and regular replacement.

    1. As of February 2017.
    Battery (Nickel-metal Hydride/Lithium-ion)

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  • Cell (Nickel-metal hydride/Lithium-ion)

    Toyota First

    Cell (Nickel-metal Hydride/Lithium-ion)

    High cell output density: the key to more compact and lightweight driveline batteries.

    Toyota First1Cell (Nickel-metal Hydride/Lithium-ion)

    High cell output density: the key to more compact and lightweight batteries.

    Cells are one of the structural units used in batteries. When multiple cells are connected and packaged to provide consistent output, voltage, and capacity, these units are generally referred to as batteries. Higher output density is greater energy output per unit of weight or volume of each cell, providing the output necessary for takeoff and acceleration. The battery in the new (2015) Prius uses higher output density cells—168 cells for nickel-metal hydride batteries and 56 cells for lithium-ion batteries. The batteries provide sufficient output, yet are more lightweight and compact.

    1. As of February 2017.
    Cell (Nickel-metal hydride/Lithium-ion)

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  • Electrical 4WD System (E-Four)

    Toyota First

    Electrical 4WD System (E-Four)

    The newly developed, high performance, compact HV4WD for compact hybrid vehicles.

    Toyota First1Electrical 4WD System (E-Four)

    The newly developed, high performance, compact HV4WD for compact hybrid vehicles.

    Unlike a mechanical 4WD system, the electrical 4WD system (E-Four) does not link the front and rear wheels with a propeller shaft, instead connecting them electrically, driving the rear wheels with motors instead of the engine. Large hybrid vehicles such as minivans use a high output E-Four system, but for the new (2015) Prius we have developed a new, compact HV4WD system for compact hybrid vehicles. It identifies when 4WD driving is needed during day-to-day use and automatically switches between front-wheel drive and four-wheel drive based on driving conditions, contributing to greater fuel efficiency.

    1. As of February 2017.
    Electrical 4WD System (E-Four)
    Our goal: The high fuel efficiency of a 2WD vehicle.

    New (2015) Prius models with HV4WD (E-Four) achieve a JC08 test-drive mode drive fuel economy rate of 34.0 km/L. This fuel efficiency exceeds even that of the third-generation Prius 2WD vehicles (32.6 km/L). The new Prius has been carefully designed to offer excellent fuel efficiency through the use of numerous drag reduction technologies.

    Fuel economy rates were determined under defined test conditions. Actual fuel economy rates may vary depending on customer usage environments (weather, traffic conditions, etc.) and driving conditions (sudden acceleration, air conditioner usage, etc.).

    Our goal: The high fuel efficiency of a 2WD vehicle.
    Repeated driving tests on the snowy roads of Tohoku and Hokkaido.

    The new (2015) Prius has undergone numerous driving tests in Tohoku and Hokkaido, areas with heavy snows, to ensure that it can drive smoothly in wheel tracks, on slopes, in parking lots, over manholes, and in other areas in which driving is difficult on snowy roads. This testing has confirmed that the new Prius offers sufficient performance for regular daily use. The reliability of its systems has been improved through thorough, intensive driving in Hokkaido.

    Repeated driving tests on the snowy roads of Tohoku and Hokkaido.
    The same spacious luggage area as found in 2WD vehicles.

    The HV4WD system unit is compact, roughly 75%2 lighter and smaller than the high output E-Four system. This makes it possible for the new (2015) Prius to offer almost the same amount of luggage space as a 2WD vehicle.

    1. Internal measurement value.
    High output E-Four/ Roughly 75% more compact

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Specifications may differ depending on country, region, or model.

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