Hybrid System

There are several ways in which electric motors and a gas/petrol engine can be combined.

Series Hybrid System

The petrol engine turns the generator. Electric power thus produced is fed to the electric motor that drives the wheels. The power flows to the wheels in series. In other words, power from the petrol engine to the electric motor is connected in series, hence the name Series Hybrid System.

Parallel Hybrid System

The wheels are driven by the petrol engine and the electric motor. The power source is selected according to the driving conditions. The name of the system comes from the fact that the power sources run in parallel.The petrol engine is the primary power source. The electric motor is used to supplement power during acceleration. However, the electric motor cannot be used to power the car while it is generating electricity.

Series/Parallel Hybrid System

With the Series Parallel Hybrid System, it is possible to drive the wheels using the dual sources of power (electric motors and/or gas/petrol engine), as well as to generate electricity while running on the electric motors. The system runs the car on power from the electric motors only, or by using both the gas/petrol engine and the electric motors together, depending on the driving conditions. Since the generator is integrated into the system, the battery can be charged while the car is running.

The basic components of the system are the electric motors, the gas/petrol engine, the generator, the power split device and the power control unit (inverter/converter). The power split device transfers part of the power produced by the gas/petrol engine to drive the wheels, and the rest to the generator to either provide electric power for the electric motors or to recharge the battery.

This system takes advantage of the energy-efficient electric motors when the car runs in the low speed range, and calls on the gas/petrol engine when the car runs in the higher speed
range. In other words, the system can control the dual sources of power for optimum energy-efficient operation under any driving conditions.

Toyota has incorporated other cutting edge technologies to improve and develop the powertrain, the generating and control systems. As a result, we are offering many benefits never before possible with a conventional powertrain.

Hybrid Vehicle

Learn more about the various technologies used in Toyota’s hybrid vehicles

Battery

World’s top level input/output to weight ratio – light weight

In addition to being light-weight, the high power output nickel metal hydride (Ni-MH) battery used in the Toyota hybrid technology provides a high input/output to weight ratio. (power output in relation to weight)

The cooling system for the battery cells including the cooling duct is optimized, while components such as the system main relay are designed for reduction in size and weight.

Furthermore, the system maintains the battery 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.

The hybrid battery (traction battery) has a limited service life. The lifespan of the hybrid battery (traction battery) can change in accordance with driving style and driving conditions.

Engine

The gas/petrol engine used in Toyota hybrid technology is more energy-efficient, producing higher output than conventional gas/petrol engines.

The new (2009) Prius’ 1.8L 2ZR-FXE high-expansion-ratio Atkinson cycle engine replaces the former 1.5L 1NZ-FXE. The wealth of torque created by an increased displacement decreases the engine rpm during high-speed cruising. Further improvements in fuel efficiency have been achieved through the following new mechanisms.

Electric water pump
The water pump is now driven by electricity from the battery. Elimination of the drive belt decreases mechanical loss, and the flow of the coolant can be controlled even more precisely according to the vehicle’s conditions.

Exhaust heat recirculation system
This system utilizes exhaust heat -what used to go wasted- for the heater and to warm up the engine, allowing quicker heater and engine warmups.

Cool-EGR system
Flow volume of the exhaust gas is controlled carefully by the electric EGR valve and is channeled into the intake manifold, alleviating negative pressure in the manifold and decreasing pumping loss in the engine. Cooling the exhaust gas with the EGR cooler actualizes large volume EGR.

Roller rocker arm
The valve train system features roller rocker arms, decreasing friction loss in valve movements.

Maximum power output: 73kW(99PS)/5,200 rpm
Maximum torque: 142N・m(14.5kgf・m)/4,000 rpm

Electric Motor

Employing synchronous A/C motor for compact packaging, light weight and high efficiency

Toyota’s hybrid technology uses synchronous A/C motors, which can efficiently produce strong torque up into the high revolution ranges and provide freedom to control motor revolutions and torque. Toyota has also succeeded in making electric motors more compact, light-weight and efficient, for smoother starts/acceleration.
– 3-phase A/C
– Optimum control of the angle between rotating magnetic field and rotor magnets
– Permanent rotor magnets positioned in the ideal V-figure configuration

Max. output:60 kW (82PS)
Max. torque:207 N・m (21.1 kgf・m)

*The figures are for Prius manufactured to Japanese market specification.

Power Split Device

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.

1. 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.
2. 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.

Regenerative Braking

Reuse of kinetic energy by using the electric motors to regenerate electricity

Toyota’s hybrid technology can reuse kinetic energy by using its electric motors to regenerate electricity in what is called “regenerative braking”.
Normally, electric motors are turned by passing an electric current through it. However, if some outside force is used to turn the electric motors, it functions as a generator and produces electricity. This makes it possible to employ the rotational force of the driving axle to turn the electric motors, thus regenerating electric energy for storage in the battery and simultaneously slowing the car with the regenerative resistance of the electric motors.

The system coordinates regenerative braking and the braking operation of the conventional hydraulic brakes so that kinetic energy, which is normally discarded as friction heat when braking, can be collected 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. Taking the Prius as an example, the system can save the energy equivalent of 1? of gas/petrol while running in city traffic for 100 km.

Generator

High speed rotation for higher maximum power output

As with electric motors, Toyota’s hybrid technology uses a synchronous AC generator capable of high speed axial rotation, realizing substantial electrical power while the car is running in the mid-speed range.
Toyota has put together the ideal generator, high output electric motor and gas/petrol engine combination to enhance low to mid-speed range acceleration.
The new Prius (2009) has a more compact, light-weight design realized through centralized winding of the coils.

Power Control Unit

Toyota’s hybrid technology is equipped with a Power Control Unit that consists of an inverter, a Voltage-Boosting Converter and an AC/DC converter to run the car on electric motors.

Inverter
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. Direct cooling of switching device is featured in the new (2009) Prius, improving cooling efficiency and enabling inverter downsizing and weight reduction.

Voltage-Boosting Converter
The Voltage-Boosting Converter steplessly increases the normal 201.6 V DC supply voltage to a maximum of 650 V to feed the electric motors and the generator 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 system efficiency. It also means that the inverter could be made smaller and lighter.

DC/DC Converter
The DC/DC converter steps down the 201.6 V supply voltage from the battery to 12 V, to be used by ancillary systems and electronic devices like the ECU.

Reduction Gear

Reduction gear amplifies torque from the electric motors

Toyota’s hybrid technology incorporates the newly developed reduction gear. The reduction gear is designed to reduce the high rpm of the front electric motors so that the power produced can be transferred to the wheels, with the added benefit of torque amplification, i.e. with greater power.This torque amplification effect, coupled with higher revving capability of the front electric motors, combines to provide seamless acceleration at will.

Plug-in Hybrid Vehicle

Learn more about the various technologies used in Toyota’s plug-in hybrid vehicles

Secondary Battery

A secondary battery is capable of storing and discharging electrical energy. Energy regenerated by the motor under deceleration is stored in the secondary battery

Plug-in hybrid vehicles are equipped with lithium-ion batteries, which have much greater capacity than conventional nickel-metal hydride batteries. Using the external battery charger, the battery is able to charge more electricity from household electrical outlets.

Electric Motor

An AC synchronous motor and a high efficiency DC brushless motor running on AC are used in plug-in hybrid vehicle. A high performance motor has been made possible through neodymium magnet (permanent magnet) combined with a laminated electromagnetic steel plate rotor. In addition, the permanent magnets are aligned in a V-shape, the optimum configuration for maximizing torque and power output. High voltage power supply also provides large amounts of electricity. All of these refinements have resulted in the creation of an electric motor with the highest level of power-to-weight and power-to-volume ratios in the world.

Max. power output: 60 kW (82 PS)
Max. torque: 207 N·m (21.1 kgf·m)

Power Control Unit

The power control unit in plug-in hybrid vehicle consists of an inverter to convert battery-supplied DC to motor-driving AC and a voltage booster circuit that increases voltage up to 650 volts. The reactor has been modified in accordance with the improved rated voltage of the battery.

Battery Charging System from an External Power Source

Plug-in hybrid vehicles come equipped with a battery charger, which allows the battery to be recharged from a household electrical outlet. Charging time is about 100 minutes at 200 VAC, and about 180 minutes at 100 VAC.

Fuel Cell Vehicle

Learn more about the various technologies used in Toyota’s fuel cell vehicles

Fuel Cell

This device generates electricity through a chemical reaction between hydrogen and oxygen. Hydrogen and ambient air are respectively supplied to the anode (negative) and the cathode (positive) of the fuel cell to generate electricity.

A fuel cell unit consists of a stack of cells called an MEA (Membrane Electrode Assembly) sandwiched between separators. The MEA is a polymer electrolyte membrane with catalyst layers applied. Since one cell can only yield less than 1 volt, several hundred cells are connected in series to increase the voltage. This combined body of cells is called a fuel cell stack (FC stack). This FC stack is commonly referred to as a fuel cell unit.

Fuel cell structure

High energy efficiency is one big advantage of using hydrogen in a fuel cell. Since it is possible to produce electricity directly from hydrogen without combustion, theoretically 83% of the energy held in a hydrogen molecule can be converted into electrical energy, which is currently more than double the energy efficiency of a gasoline powered engine.

Mechanism of electricity generation from hydrogen and oxygen in a fuel cell

1. Hydrogen is supplied to the anode side.
2. Hydrogen molecules activated by the anode catalyst release electrons.
3. The electrons released from hydrogen travel from the anode to the cathode, creating an electrical current.
4. Hydrogen molecules that released electrons become hydrogen ions and move through the polymer electrolyte membrane to the cathode side.
5. Hydrogen ions bond with airborne oxygen and electrons on the cathode catalyst to form water.

Secondary Battery

A secondary battery is capable of storing and discharging electrical energy. Energy regenerated by the motor under deceleration is stored in the secondary battery

The TOYOTA FCHV-adv is equipped with a nickel-metal hydride battery with a maximum power output of 21 kW. Regenerated energy under deceleration is stored in this secondary battery and supplements power from the fuel cell by providing auxiliary power under acceleration.

Electric Motor

An AC synchronous motor developed by Toyota is used in the TOYOTA FCHV-adv. This motor functions as a generator under deceleration to regenerate energy.

Max. power output: 90 kW (122 PS)
Max. torque: 260 N·m (26.5 kgf·m)

Power Control Unit

The power control unit in the TOYOTA FCHV-adv consists of an inverter that converts DC into AC to power the motor and a DC/DC converter that draws current from and recharges the secondary battery, among other systems. It exercises precision control over fuel cell power output and secondary battery discharge and recharge under all driving conditions.

High-pressure Hydrogen Tank

A 70 MPa high-pressure hydrogen tank developed by Toyota is installed in the TOYOTA FCHV-adv. The latest 70 MPa tank features a polyamide resin liner in the inner most layer of the tank due to its high strength and excellent hydrogen permeation prevention performance. Increased tank capacity and reduced weight have been achieved by using optimum materials, improving design and production methods, and minimizing wall thickness by optimizing the winding angle, tension and volume of the carbon fiber. This has contributed to significant improvement in cruising range.