Ordinary power trains waste energy at stoplights, during braking, and at all other times when the engine is not running at optimum speed under ideal load conditions.
By reducing energy wastage and applying energy more efficiently, a hybrid system can simultaneously double fuel economy, slash emissions and deliver "fun to drive" performance.
WHAT IS A HYBRID SYSTEM?
A hybrid system combines different power sources to maximise each one's strengths, while compensating for each other's shortcomings. A petrol-electric hybrid system, for example (as used in the Toyota Prius), 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 to charge.
HOW IT WORKS:
Only the electric motor is used for start-up and low to mid-range speeds.
When cruising, the engine and motor both drive the wheels: engine power is split between the wheels and an electric generator, which in turn drives the electric motor. Power allocation is controlled to maximise efficiency. As necessary, the generator also recharges the battery from surplus engine power.
The battery supplies additional energy to boost drive power. The engine and motor together provide smooth acceleration response.
The high-output motor acts as a high-output generator, driven by the car's wheels. This "regenerative braking system" recovers kinetic energy as electrical energy, which is stored in the high-performance battery.
The "Hybrid Synergy Drive" system applied in the Prius combines the best features of a petrol engine with those of a battery powered system but with only one power source - petrol. The electrical side of the system does not need to be independently recharged.
ELEMENTS OF THE TOYOTA HYBRID SYNERGY DRIVE SYSTEM
High Expansion Ratio Atkinson Cycle Petrol Engine
The Prius engine operates at optimum speed for high efficiency. This 1.5-litre engine also extracts more energy from petrol combustion by using the high expansion Atkinson Cycle.
To charge the battery and supply power to the high-output motor, the generator is run at speeds of up to 10 000 r/min. This improves acceleration at low and medium speed.
The sealed, maintenance free nickel-metal hydride (Ni-MH) battery is a compact, high power density unit. It is charged by the engine via the generator at cruising speed, and by the motor during regenerative braking.
Power Control Unit (Inverter)
The Power Control Unit contains an inverter that converts DC (Direct Current) from the battery into AC (Alternating Current) for the driving motor. Its high voltage power circuit raises the power supply to 500 volts, almost double that used in the previous generation Prius hybrid system.
Instead of wasting energy as heat dissipated from the braking system, the regenerative braking system uses the motor as a generator to convert braking energy into electricity that is stored in the battery. This system is particularly effective in stop-start city driving.
The high output, permanent-magnet electric motor features neodymium magnets in an optimum V shape to produce 50kW and loads of torque at 500 volts. Latest technology has seen a 1.5 fold improvement over the initial Prius hybrid system.
Power Split Device
This splits power from the engine into two routes: mechanical and electrical. A planetary gear system can transfer power between engine, motor, generator, and wheels in almost any combination. The power split device is also known as the "hybrid transaxle".
ARE ALL HYBRIDS CREATED EQUAL?
Toyota has perfected the series/parallel or "strong" hybrid to deliver the energy saving benefit of a series hybrid together with the acceleration benefit of a parallel hybrid. Two key technologies - the power split device and sophisticated energy management - make this possible. They constantly optimise the flows of mechanical power and electric power for safe and comfortable vehicle operation at the highest possible efficiency.
THREE KINDS OF HYBRID
Electric motor drives wheels; engine's only task is to generate electricity.
Engine is the main source of power to the wheels; the motor assists with acceleration.
Series/Parallel Hybrid (Prius):
"Power split device" delivers a continuously variable ratio of engine/motor power to wheels. Can run in "stealth mode (EV)" on its stored electricity alone.
GOALS OF HYBRID SYNERGY DRIVE DEVELOPMENT
In developing Hybrid Synergy Drive, Toyota sought ways to strengthen engine and motor power, raise electric power, and improve energy management for more efficient and effective control of the energy made available. The benefits are world leading environmental performance and more powerful acceleration for a higher "fun to drive" quotient.
A MORE POWERFUL SYNERGY
In a conventional power train there is a trade off between power and efficiency. If you try to raise one, you reduce the other. All things being equal, the larger your engine, the higher your fuel consumption. Hybrid Synergy Drive rearranges this relationship. Instead of compromising or sacrificing, it seeks synergies.
In the new Prius, Hybrid Synergy Drive achieves a more powerful synergy by boosting the hybrid system's voltage to a maximum of 500 volts (up from 274 in the first generation Prius). A higher voltage means that electrical power can be supplied to the motor using a smaller current to increase efficiency. Or, if current is kept the same, the higher voltage can be used to raise power.
MORE FUN TO DRIVE
In addition to its high voltage power circuit, Hybrid Synergy Drive also employs a higher-performance battery and higher speed motor and generator than previous hybrid technologies. Together with enhanced energy management, these enable 1,5 times the motor power of Toyota's earlier Hybrid system used in the first generation Prius, while attaining even greater fuel efficiency.
Side benefits include "torque on demand", an innovation that provides added traction on slick roads by taking advantage of the power split device.
For the driver, the combination of greater motor power and engine power, plus greater control in Hybrid Synergy Drive, provides a more powerful, smoother and safer driving experience.
WHY? HOW? WHEN?
The Toyota Initiative
Hybrid technology's potential is becoming clearer by the day. Toyota does not regard hybrid technology as simply a steppingstone to the age of fuel cell vehicles. The company sees it as the core technology that will become dominant in the eco-car market and eventually evolve to form the basis of what we call the "ultimate eco-car."
Toyota has a long history of continuous improvement when it comes to conventional engines, including lean burn petrol engines, direct-injection petrol engines, and common rail direct-injection diesel engines, as well as engines modified to use alternative fuels, such as compressed natural gas (CNG) or electricity (EV).
In December 2002 the company began the limited sale of the Toyota FCHV, a Fuel Cell Hybrid Vehicle that runs on high-pressure hydrogen.
Toyota concedes that its engineers may disagree about which fuel or car propulsion system is best. But they do agree that hybrid technology is the core for eco-car development.
Toyota develops key eco-technologies in-house to reduce costs and rapidly commercialise its applications.
One of the yardsticks used to assess the environmental cost of a future technological scenario is the well-to-wheel efficiency. This expresses the overall efficiency of an energy source, from extraction to when it turns a vehicle's wheels.
Well-to-wheel calculations illustrate that, regardless of power source, Toyota's hybrid technologies increase efficiency substantially.
A STRATEGY FOR LIFE
Hybrid technology is a rediscovery of an energy strategy that living things depend on. Humans and other animals store energy temporarily so that they can access it quickly when needed.
Like our metabolic system, Toyota's hybrid technology saves fuel by storing energy and adjusting intelligently to each situation.
A high performance battery stores energy that is ordinarily wasted while driving or stopping, and applies the stored energy when starting and to supplement engine power when accelerating. Since the system recharges itself, it never needs to be plugged in to charge.
HYBRID - PAST, PRESENT, FUTURE
A "strong hybrid" system like Hybrid Synergy Drive can use its petrol engine and electric motor in any combination, and even run only on its stored electricity.
Toyota has also created other kinds of hybrid vehicles to help lighten the environmental load in every way possible.
The latest Toyota SU-HV1 concept features a Hybrid Synergy Drive application optimised for the large displacement and output of a V6 engine. It uses a faster 120kW front motor and a 50kW rear motor for higher torque and higher output with a more powerful electrical system. A V6 (3,3 litre) engine using this technology can deliver larger displacement V8 performance, with fuel efficiency and emissions at compact car levels, twice as good as those of a conventional SUV of equal displacement.
Toyota is committed to developing further applications of hybrid technology because of the company's belief that this is a core automotive technology. Toyota's hybrid systems can be integrated with many kinds of propulsion systems - not just petrol engines, but also diesel engines, alternative energy vehicles, and fuel cell vehicles.
Toyota's Hybrid Synergy Drive technology is robust, powerful and flexible enough to enhance the environmental and driving performance of virtually any type of car, from family sedans to minivans and luxury vehicles.
The Prius is really just the beginning. Toyota's hybrid technology is set to continue to evolve way into the future.
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