Automobile hybrid systems combine two motive power sources, such as an internal combustion engine and an electric motor, to take advantage of the benefits provided by these power sources while compensating for each other's shortcomings, resulting in highly efficient driving performance. Although hybrid systems use an electric motor, they do not require external charging, as do electric vehicles.
Hybrid systems possess the following four characteristics:
1) Energy-loss reduction
The system automatically stops the idling of the engine (idling stop), thus reducing the energy that would normally be wasted.
2) Energy recovery and reuse
The energy that would normally be wasted as heat during deceleration and braking is recovered as electrical energy, which is then used to power the starter and the electric motor.
3) Motor assist
The electric motor assists the engine during acceleration.
4) High-efficiency operation control
The system maximizes the vehicle's overall efficiency by using the electric motor to run the vehicle under operating conditions in which the engine's efficiency is low and by generating electricity under operating conditions in which the engine's efficiency is high.
The series/parallel hybrid system has all of these characteristics and therefore provides both superior fuel efficiency and driving performance.
There are three types of Hybrid systems from Toyota. The following three major types of hybrid systems are being used in the hybrid vehicles currently on the market:
1) Series hybrid system
The engine drives a generator, and an electric motor uses this generated electricity to drive the wheels. This is called a series hybrid system because the power flows to the wheels in series, i.e., the engine power and the motor power are in series. A series hybrid system can run a small-output engine in the efficient operating region relatively steadily, generate and supply electricity to the electric motor and efficiently charge the battery. It has two motors, a generator (which has the same structure as an electric motor) and an electric motor. This system is being used in the Coaster Hybrid.
2) Parallel hybrid system
In a parallel hybrid system, both the engine and the electric motor drive the wheels, and the drive power from these two sources can be utilized according to the prevailing conditions. This is called a parallel hybrid system because the power flows to the wheels in parallel. In this system, the battery is charged by switching the electric motor to act as a generator, and the electricity from the battery is used to drive the wheels. Although it has a simple structure, the parallel hybrid system cannot drive the wheels from the electric motor while simultaneously charging the battery since the system has only one motor.
3) Series/parallel hybrid system
This system combines the series hybrid system with the parallel hybrid system in order to maximize the benefits of both systems. It has two motors, and depending on the driving conditions, uses only the electric motor or the driving power from both the electric motor and the engine, in order to achieve the highest efficiency level. Furthermore, when necessary, the system drives the wheels while simultaneously generating electricity using a generator. This is the system used in the Prius and the Estima Hybrid.
Since a series hybrid uses its engine to generate electricity for the motor to drive the wheels, the engine and motor do about the same amount of work.
A parallel hybrid uses the engine as the main power source, with the motor used only to provide assistance during acceleration. Therefore, the engine is used much more than the motor.
In a series/parallel hybrid (THS in the Prius), a power split device divides the power from the engine, so the ratio of power going directly to the wheels and to the generator is continuously variable. Since the motor can run on this electric power as it is generated, the motor is used more than in a parallel system.
Panasonic Advanced Hybrid System
A hybrid system combines different power sources to maximize each one's strengths, while compensating for each other's shortcomings. A gasoline-electric hybrid system, for example, combines an internal combustion engine's high-speed power with the clean efficiency and low-speed torque of an electric motor that never needs to be plugged in for recharging.
Toyota is working to not only further enhance the convenience of its vehicles but is also focusing its initiatives on solving global environmental issues through a variety of activities and proposals for realizing sustainable mobility. The development of powertrain technology is the basis for improving the environmental performance of vehicles, and this technology is being developed from three perspectives: 1) improving fuel efficiency in order to reduce CO2 emissions, 2) making exhaust emissions cleaner to help abate atmospheric pollution, and 3) pursuing energy diversification.
Toyota strives, in its move towards energy diversification, to provide the necessary vehicle at the time and place it is needed, i.e. the right vehicle at the right time and in the right place. In addition, Toyota is actively developing hybrid technology to serve as a core technology applicable to all powertrains.
Toyota's mission has always been to provide clean and safe products. Thus, the company has positioned the environment as one of its most important issues and has been working toward creating a prosperous society and a world that is comfortable to live in. With this goal in mind, Toyota has been actively developing various new technologies from the perspective of achieving energy security and diversifying energy sources, which is necessitated by the dwindling supply of petroleum resources.
For example, in motive power sources for automobiles alone, we have been continuously improving conventional engines and have developed and commercialized lean-burn gasoline engines, direct injection gasoline engines and common rail direct-injection diesel engines, etc. We have also been modifying engines so that they can use alternative fuels, such as compressed natural gas (CNG), instead of gasoline or light oil, and have been installing these engines in commercially sold vehicles.
Toyota has also developed and has been marketing electric vehicles (EV) that use motors for the driving source; hybrid vehicles (HV) that combine an engine and a motor, fusing the advantages of these two power sources; fuel cell hybrid vehicles (FCHV) that use fuel cells (FC) to generate electricity based on a chemical reaction between hydrogen and the oxygen in the air and that supply this electricity to electric motors to produce driving power.
In January 1997, Toyota declared the start of the Toyota Eco Project. As part of this effort, Toyota decided to tackle the international challenge of reducing CO2 emissions in order to prevent global warming and accelerated the development of a hybrid vehicle with the goal of achieving twice the fuel efficiency of conventional vehicles. Then, in March of the same year, Toyota announced the completion of a new power train called the Toyota Hybrid System (THS) for use in passenger vehicles.
This power train combines a gasoline engine and an electric motor, and because it does not require external charging, as do existing electric vehicles, it works within existing infrastructures such as fueling facilities. This system also achieves nearly twice the fuel efficiency of conventional gasoline engines.
THS was installed in the passenger vehicle Prius, which was introduced in December 1997 in the Japanese market as the first mass-produced hybrid passenger vehicle in the world. In 2000, overseas marketing of the Prius began. The Prius has gained a reputation as a highly innovative vehicle, and its cumulative worldwide sales have exceeded 110,000 units.
Meanwhile, THS has continued to evolve, and in 2001, THS-C, which combines THS with CVT (continuously variable transmission), was installed in the Estima Hybrid minivan and THS-M (a mild hybrid system) was installed in the Crown, luxury sedan, both for the Japanese market thereby contributing greatly to innovations in the automobiles of the 21st century.
Building on the ecology-focused THS, Toyota has developed the concept of Hybrid Synergy Drive. Based on this concept, Toyota has developed a new-generation Toyota hybrid system called THS II, which achieves high levels of compatibility between environmental performance and power by increasing the motor output by 1.5 times, greatly boosting the power supply voltage and achieving significant advances in the control system, aiming for synergy between motor power and engine power.
Toyota has positioned hybrid technology as its key technology. Beginning with the development of EVs and through the commercialization of HVs and FCHVs, its continued efforts have now culminated in the development of THS II. Toyota will continue to endeavor to make technical advances in this area.
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