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Technology File - Safety Technology

Fuel Cell Vehicle

Introducing the technologies used in Toyota’s fuel cell vehicles.

  • AFC Stack
  • BHydrogen System
  • CAir System
  • DCooling System)
  • EFC Boost Converter
  • FBattery (Nickel-metal Hydride)
  • GMotor
  • HPower Control Unit

HV

Toyota Fuel Cell System

Fuel cells and a hybrid system are the power sources of the Mirai.

The Toyota Fuel Cell System (TFCS), the power train of the MIRAI, is a highly efficient system that integrates the fuel cell technologies and the hybrid ……

Toyota Fuel Cell System

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FC Stack

Toyota First1<Volume Power Density> Global Top Level2Column

Hundreds of cells are stacked, creating a small power plant.

The fuel cell (FC) stack is a power generating device that produces electricity by using a chemical reaction between hydrogen and oxygen in the air. ……

FC Stack

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Cooling System

Design cleverly cools the system and promotes air flow.

Two independent cooling systems are used—a FC cooling system that uses cooling fluid just for the FC to cool the FC stack, and an EV cooling system ……

Cooling System

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FC Boost Converter

Boosting the electric power produced by hydrogen and air (oxygen).

The FC boost converter is a device for boosting the electric power generated by the fuel cell at higher voltage (approximately 650 V). Toyota developed ……

FC Boost Converter

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Battery (Nickel-metal Hydride)

The battery provides the energy necessary for acceleration and withstands cold.

The battery stores energy recovered during deceleration and assists output from the FC stack during acceleration. The Mirai is equipped with a ……

Battery (Nickel-metal Hydride)

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Motor

Toyota First1

A more highly evolved motor for even greater driving enjoyment.

Like Toyota’s hybrid vehicles, the Mirai uses a synchronous AC motor. This synchronous AC motor efficiently generates a large amount of torque from ……

Motor

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Power Control Unit

The brain of the fuel cell vehicle, expertly controlling electricity.

The power control unit converts AC/DC power and appropriately adjusts the electrical voltage. The Mirai power control unit consists of an inverter, ……

Power Control Unit

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  • Toyota Fuel Cell System

    Toyota Fuel Cell System

    Fuel cells and a hybrid system are the power sources of the Mirai.

    Toyota Fuel Cell System

    Fuel cells and a hybrid system are the power sources of the Mirai.

    The Toyota Fuel Cell System (TFCS1), the power train of the MIRAI, is a highly efficient system that integrates the fuel cell technologies and the hybrid technologies cultivated by Toyota. At its core is Toyota’s first mass-produced fuel cell, the Toyota FC Stack. Two energy sources are used optimally to drive the motor: the fuel cell (FC) stack, which generates electricity by the chemical reaction of water and oxygen, and the battery. The system generates electric power for driving the vehicle and emits only water as a powerful and clean power source.

    1. TFCS:Toyota Fuel Cell System
    Toyota Fuel Cell System
    Operating principals
    1. STEP 1. Air (oxygen) taken in
    2. STEP 2. Oxygen and hydrogen supplied to fuel cell stack
    3. STEP 3. Electricity and water generated through chemical reaction
    4. STEP 4. Electricity supplied to motor
    5. STEP 5. Motor is activated and vehicle moves
    6. STEP 6. Water emitted outside vehicle
    A. Motor, B. Fuel cell stack, C. Battery, D. High-pressure hydrogen tank

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  • FC Stack

    Toyota FirstGlobal Top LevelColumn

    FC Stack

    Hundreds of cells are stacked, creating a small power plant.

    Toyota First1<Volume power density> Global Top Level2FC Stack

    Hundreds of cells are stacked, creating a small power plant.

    The fuel cell (FC) stack is a power generating device that produces electricity by using a chemical reaction between hydrogen and oxygen in the air. Hydrogen is supplied to a negative electrode (anode) and air (oxygen) is supplied to positive electrode (cathode), generating electric power in an opposite reaction of electrolysis. The FC stack comprises hundreds of stacked components called cells. Each cell consists of a membrane electrode assembly (MEA), which is a solid polymer electrolyte membrane coated with catalyst on both sides (electrodes), sandwiched between separators. The voltage of a single cell is less than 1 V, and consequently, the voltage is increased by stacking hundreds of cells in series. The cells are stacked in this manner to create a single FC stack, also known as a fuel cell stack (a “fuel cell” generally refers to an FC stack or fuel cell stack).

    Innovations to the cell flow channel structure and electrodes of the Mirai FC stack produce a power density of 3.1 kW/L, which is at that world’s highest level. This enabled miniaturization of the FC stack, making it possible to install the FC stack below the floor of a sedan and create a spacious vehicle interior.

    1. As of November 2014.
    2. As of November 2014. According to Toyota Motor Corporation.
    FC Stack
    Main specifications of the Mirai FC stack
    Maximum output 114 kW (155PS)
    Volume power density 3.1 kW/L (global top level)
    Number of cells in one stack 370 cells (single-line stacking)

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  • Principle of Power Generation by Fuel Cells

    Principle of Power Generation by Fuel Cells

    H2+½O2→H₂O generates electricity.

    Principle of Power Generation by Fuel Cells

    H2+½O2→H₂O generates electricity.

    When electricity is applied to water, hydrogen and oxygen are produced. This is referred to as the electrolysis of water. A fuel cell uses the opposite reaction whereby hydrogen and oxygen in the air react to produce electricity and water. A key feature of fuel cells that use hydrogen is high energy efficiency. Since electric power is generated directly without burning hydrogen, it is theoretically possible to convert 83% of the energy in the hydrogen to electrical energy. This is approximately double the efficiency of current gasoline engines.

    Principle of Power Generation by Fuel Cells
    How electricity is generated from hydrogen and oxygen in a fuel cell
    1. Hydrogen is supplied to the anode side. (negative electrode)
    2. Hydrogen molecules activated by the anode catalyst release their electrons.
    3. The released electrons travel from the anode to the cathode, creating an electrical current.
    4. The hydrogen molecules that release electrons become hydrogen ions and move through the polymer electrolyte membrane to the cathode side.
    5. The hydrogen ions bond with airborne oxygen and electrons on the cathode catalyst to form water. (positive electrode)

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  • Types of Fuel Cells

    Types of Fuel Cells

    There are more than one type of fuel cells.

    Types of Fuel Cells

    There are more than one type of fuel cells.

    Fuel cells are broadly divided into five categories. Each category has its own characteristics, and are selected according to the application. Alkaline fuel cells, for example, are used for space applications. They operate at room temperature and are easy to handle, but unfortunately, they cannot function in the presence of carbon dioxide. As a result, they are difficult to use on the earth’s surface, but there is no problem using them in outer space or on a submarine. Phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells are used in large generators and cogeneration systems that operate at high temperatures ranging from 200°C to 1,000°C.
    The polymer electrolyte fuel cells operate at temperatures of approximately 60-80°C, making them the ideal fuel cell for use in automobiles.

    Types of Fuel Cells

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  • Freeze Starting

    Column

    Freeze Starting

    Fuel cells operate without freezing even at sub-zero temperatures.

    Freeze Starting

    Fuel cells operate without freezing even at sub-zero temperatures.

    If the water produced during the electric power generating process freezes inside the fuel cell, there is a risk that the supply of hydrogen and oxygen as well as the release of water will not function efficiently, resulting in a decline in power generating performance. To prevent this, the amount of water in the FC stack is controlled, increasing power generating performance immediately after starting at sub-zero temperatures. In addition, warm-up time is greatly reduced by increasing the amount of heat generated by the fuel cell. These strategies make it possible to start up smoothly even below the freezing point.

    Freeze Starting

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  • Cells

    Column

    Cells

    Electric power is generated from the chemical reaction of hydrogen and air (oxygen).

    Cells

    Electric power is generated from the chemical reaction of hydrogen and air (oxygen).

    Cells are generally made from electrolyte membrane, a pair of electrodes (a negative electrode and a positive electrode), separators, and other components. The voltage of a single cell is less than 1 V, but the voltage is increased by stacking hundreds of cells in series, generating the substantial electric power needed to operate a motor vehicle.

    Cells

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  • 3D Fine-mesh Flow Field

    Global FirstColumn

    3D Fine-mesh Flow Field

    A three-dimensional zig-zag structure improves fluid drainage and increases generating efficiency.

    Global First13D Fine-mesh Flow Field

    A three-dimensional zig-zag structure improves fluid drainage and increases generating efficiency.

    The 3D fine-mesh flow field employs a flow field on the positive (air) electrode of the cell. The world’s first 3D fine-mesh structure increases water drainage and provides a uniform supply of air to the cell surface. As a result, the Mirai achieves 2.4 times the current density of earlier vehicles. This contributes substantially to generating efficiency at the world’s highest level.

    1. As of November 2014. According to Toyota Motor Corporation.
    3D Fine-mesh Flow Field

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  • High-pressure Hydrogen Tanks

    Global Top Level

    High-pressure Hydrogen Tanks

    Proprietary three-layer structure increases strength and durability.

    <Storage Density>Global Top Level1High-pressure Hydrogen Tanks

    Proprietary three-layer structure increases strength and durability.

    High-pressure hydrogen tanks store the hydrogen that is used as fuel at a high pressure of approximately 70 MPa. Toyota adopted a three-layer structure (a plastic liner that seals in hydrogen, a carbon-fiber reinforced plastic layer that provides pressure resistance strength, and a fiberglass reinforced plastic layer that protects the outer surface) to enhance storage performance and safety. The carbon-fiber reinforced plastic in particular is so strong that it is used in the latest aircraft components. In addition, innovative improvements made to the layering pattern made it possible to make the tank more compact and lightweight, achieving one of the world’s best tank storage performances1 at 5.7 wt%.

    1. Hydrogen storage capacity compared to tank weight (percentage of weight). As of November 2014. According to Toyota Motor Corporation.
    High-pressure Hydrogen Tanks

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  • Hydrogen Circulating Pump

    Hydrogen Circulating Pump

    Hydrogen is used as a precious energy source without any left over.

    Hydrogen Circulating Pump

    Hydrogen is used as a precious energy source without any left over.

    The hydrogen circulating pump recirculates any hydrogen that did not react during electric power generation, effectively using the hydrogen. In addition, the flow of gas on the hydrogen side in the cells transports water downward, humidifying the intake on the air side, which is susceptible to drying. This makes it possible to eliminate the external humidifier. In addition, integrating the hydrogen circulating pump with the FC stack improves heat dissipation and makes it more compact and lightweight.

    Hydrogen Circulating Pump

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  • Hydrogen Fueling

    Hydrogen Fueling

    Rapid hydrogen fueling allows for long drives without stopping.

    Hydrogen Fueling

    Rapid hydrogen fueling allows for long drives without stopping.

    Hydrogen fueling is performed at hydrogen stations, which are spreading to various regions. It takes about three minutes to refuel1, and a full tank provides about the same range as a gasoline vehicle. The Mirai is compatible with common new fueling standards2 in Japan, the United States and Europe.

    1. Toyota measurement under SAEJ2601 standards (ambient temperature: 20°C, hydrogen tank pressure when fueled: 10 MPa). Fueling time varies according to hydrogen fueling pressure and ambient temperature.
    2. Fueling equipment: ISO 17268: Gaseous Hydrogen Land Vehicle Refueling Connection Devices
      Fueling method: SAE J2601: Fueling Protocols for Light Duty Gaseous Hydrogen Surface Vehicles
      Fueling communications: SAE J2799: 70 MPa Compressed Hydrogen Surface Vehicle Fueling Connection Device and Optional Vehicle to Station Communications
    Hydrogen Fueling

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  • Hydrogen Safety

    Hydrogen Safety

    We are rigorously examining safety from three perspectives.

    Hydrogen Safety

    We are rigorously examining safety from three perspectives.

    Hydrogen is a fuel that can be used safely, just like gasoline, if handled properly. The Mirai was designed based on comprehensive safety measures with preventing hydrogen leaks, detecting and stopping leaks, and preventing the accumulation of hydrogen as the core concepts. In addition, a high degree of collision safety is achieved to protect the FC stack and high-pressure hydrogen tank from deformation caused by shock and deformation of the vehicle body in the event of a collision.

    Hydrogen Safety
    Measures to prevent leaks

    Extremely reliable high-pressure hydrogen tank with outstanding strength and durability.

    High-pressure hydrogen tank (three-layer structure)
    Surface layer Fiberglass reinforced plastic
    Middle layer Carbon fiber-reinforced plastic
    Interior layer Plastic liner
    High-pressure hydrogen tank (three-layer structure)
    Measures to detect and stop leaks

    Hydrogen detectors are installed to detect any leaks. If a hydrogen leak or a collision is detected, the tank valve is shut off (if the concentration is low, a warning is issued).

    Measures to detect and stop leaks
    Hydrogen leak warning display (on the dashboard)
    Structure that prevents accumulation

    Placement of hydrogen system components outside the vehicle cabin facilitates the dispersion of hydrogen.

    Structure that prevents accumulation

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  • Air Compressor (Six-lobe Helical Root Type Rotor)

    Global FirstColumn

    Air Compressor (Six-lobe Helical Root Type Rotor)

    Large amounts of air are drawn in and pumped to the FC stack.

    Global First1Air Compressor (Six-lobe Helical Root Type Rotor)

    Large amounts of air are drawn in and pumped to the FC stack.

    The air compressor (six-lobe helical root type rotor) compresses the air necessary for electric power generation and pumps it to the FC stack. The amount of air needed by the FC stack varies from an extremely small flow when the vehicle is idling to a very large flow when accelerating. The Mirai uses a proprietary six-lobe helical root type rotor—a world’s first—to efficiently draw in and compress air according to the volume of air flowing in. This contributes to enhancing the powerful acceleration and cruising range.

    1. As of November 2014. According to Toyota Motor Corporation.
    Air Compressor (Six-lobe Helical Root Type Rotor)

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  • Internal Humidification (No External Humidifier)

    Global First

    Internal Humidification (No External Humidifier)

    Water produced in the stack is not just removed, but is used effectively.

    Global First1Internal Humidification (No External Humidifier)

    Water produced in the stack is not just removed, but is used effectively.

    For a fuel cell to generate electricity, it is necessary that the electrolyte membrane be suitably wet so that hydrogen ions in the electrolyte membrane can move smoothly. The general approach to achieving this was to recover water in the exhaust gas of the fuel cell and supply the water to the intake air by external humidifier, but the Mirai circulates water produced from electric power generation within the stack. The water is effectively used through such self-humidification. This made it possible for Toyota to create the world’s first fuel cell without an external humidifier, making the fuel cell system more compact and lighter.

    1. As of November 2014. According to Toyota Motor Corporation.
    Internal Humidification (No External Humidifier)
    1. <Thinner electrolyte membrane> Promotes back-diffusion of generated water.
    2. <Increased hydrogen circulation volume> Increased water vapor supply from the anode upstream to downstream.
    3. <Humidification from anode> Air and hydrogen flow in opposite directions, humidifying upstream air flow, which tends to dry out.
    4. <Suppression of evapotranspiration> Increases coolant water volume in upstream air and suppresses temperature increase and also suppresses evapotranspiration of generated water.

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  • Cooling System

    Cooling System

    Design cleverly cools the system and promotes air flow.

    Cooling System

    Design cleverly cools the system and promotes air flow.

    Two independent cooling systems are used—a FC cooling system that uses cooling fluid just for the FC to cool the FC stack, and an EV cooling system that cools the inverter and motor system.

    The FC cooling system uses a pump to circulate cooling fluid between a radiator and the fuel cell, similar to the cooling system of a conventional engine automobile, to prevent the temperature of the FC stack from increasing too much from the heat produced when the fuel cell generates electricity. In order to prevent short circuits from the FC stack via the cooling fluid, an ion exchanger is also used to ensure that the cooling fluid is non-conducting.

    Cooling System FC water pump
    FC water pumpCirculates cooling fluid to cool the FC stack.
    Radiator
    RadiatorCools the FC stack by dissipating the heat of cooling fluid.
    Concept of Aerodynamic Performance Development
    Concept of aerodynamic performance development
    1. Aerodynamic and cooling performance
      Smooth merging of radiator exhaust flows with airflows at the side and under the vehicle.
    2. Aerodynamic performance and FCV package
      Optimization of airflows under the vehicle to achieve smooth outflow from the rear and smooth merging with upper surface airflows.
    3. Aerodynamic performance and advanced exterior styling
      Prevention of airflow separation at the front and optimization of airflow at the sides.

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  • FC Boost Converter

    FC Boost Converter

    Boosting the electric power produced by hydrogen and air (oxygen).

    FC Boost Converter

    Boosting the electric power produced by hydrogen and air (oxygen).

    The FC boost converter is a device for boosting the electric power generated by the fuel cell at higher voltage (approximately 650 V). Toyota developed a high-capacity FC boost converter. This made it possible to reduce the number of cells in the FC stack while using the same motors, inverters, and other components used in current mass-production hybrid units, significantly cutting costs and raising reliability. In addition, innovations to the voltage boosting control and case structure provide exceptionally quiet operation.

    FC Boost Converter

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  • Battery (Nickel-metal Hydride)

    Battery (Nickel-metal Hydride)

    The battery provides the energy necessary for acceleration and withstands cold.

    Battery (Nickel-metal Hydride)

    The battery provides the energy necessary for acceleration and withstands cold.

    The battery stores energy recovered during deceleration and assists output from the FC stack during acceleration. The Mirai is equipped with a nickel-metal hydride battery that is mature both technologically and as a product. The battery features exceptional performance in terms of usability and durability at extremely low temperatures.

    Battery (Nickel-metal Hydride)

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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.

    Like Toyota’s hybrid vehicles, the Mirai uses a synchronous AC motor. 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 high-speed motor uses a new coil winding method, producing greater output density in a more compact, lightweight motor. Together with the dual-axle structure, this compact design contributes more freedom of component integration.

    1. As of February 2017.

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

    Motor

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  • Power Control Unit

    Power Control Unit

    The brain of the fuel cell vehicle, expertly controlling electricity.

    Power Control Unit

    The brain of the fuel cell vehicle, expertly controlling electricity.

    The power control unit converts AC/DC power and appropriately adjusts the electrical voltage. The Mirai power control unit consists of an inverter, a boost converter, and a DC/DC converter. The unit precisely controls the FC stack output and battery charging and discharging under all operating conditions.

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

    Power Control Unit
    Inverter

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

    Motors cannot be operated by connecting them directly to the battery. The inverter converts DC supplied from the battery to AC to turn the electric motors. Conversely, it converts AC generated by the electric motors during deceleration into DC to recharge the battery. Dual side cooling, which directly cools power elements, improves cooling efficiency and enables inverter downsizing and weight reduction.

    Boost converter

    Controlling voltage and boosting low voltages.

    The boost converter controls charging and discharging electricity by adjusting the voltage of the battery. It steplessly increases the normal roughly 250 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 applications other than driving.

    The DC/DC converter steps down the supply voltage from the high voltage battery. It steps down the roughly 250 V DC supply voltage from the battery to 12 V DC, to be used by engine auxiliary systems which assist with FC system operation and electronic devices such as headlights.

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

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