Gas or petrol engines have certain strength - and weakness. So do electric motors. Toyota combines the best of both to create the world's best hybrids.
Toyota's full hybrid system uniquely combines electric motor with gasoline engine to create one of the world's most efficient vehicles. Here's how.
Taking advantage of the electric motors' low-speed torque at start-off
When the car starts off, Toyota's hybrid vehicles use only the electric motors, powered by the battery, while the gas/petrol engine remains shut off. A gas/petrol engine cannot produce high torque in the low rpm range, whereas electric motors can - delivering a very responsive and smooth start.
Energy-efficient motor-driven running
A gas/petrol engine is not energy efficient in running a car in the low-speed range. On the other hand, electric motors are energy efficient in running a car in the low-speed range.
Therefore, Toyota's hybrid vehicles use the electric energy stored in its battery to run the car on the electric motors in low-speed range.
*If the battery charge level is low, the gas/petrol engine is used to turn the generator to supply power to the electric motors.
Energy-efficient driving, using the gas/petrol engine as the main power source
Toyota's hybrid vehicles use the gas/petrol engine in the speed range in which it operates with good energy efficiency.
The power produced by the gas/petrol engine is used to drive the wheels directly, and depending on the driving conditions, part of the power is distributed to the generator. Power produced by the generator is used to feed the electric motors, to supplement the gas/petrol engine.
By making use of the engine/motor dual powertrain, the energy produced by the gas/petrol engine is transferred to the road surface with minimal loss.
*If the battery charge level is low, the power output from the gas/petrol engine is increased to increase the amount of electricity generated to recharge the battery.
Recharging the battery with surplus energy
Since Toyota's hybrid vehicles operate the gas/petrol engine in its high efficiency range, the gas/petrol engine may produce more power than is necessary to drive the car. In this case, the surplus power is converted to electric energy by the generator to be stored in the battery.
Dual power for acceleration one class higher
When strong acceleration is called for (e.g, for climbing a steep slope or overtaking) the power from the battery is supplied to the electric motors to supplement driving power. By combining the power from the gas/petrol engine and the electric motors, Toyota's hybrid vehicles deliver power comparable to cars having one class larger engine displacement of one class higher.
Storing regenerated energy under deceleration in the battery
Under braking or when the accelerator is lifted, Toyota's hybrid vehicles use the kinetic energy of the car to let the wheels turn the electric motors, which function as regenerators. Energy that is normally lost as friction heat under deceleration is converted into electrical energy, which is recovered in the battery to be reused later.
Shutting down entire powertrain when the car is at rest
The gas/petrol engine, the electric motors and the generator are automatically shut down when the car comes to rest. No energy is wasted by idling.
*If the battery charge level is low, the gas/petrol engine is kept running to recharge it. In some cases, the gas/petrol engine may be turned on in conjunction with the air-conditioner switch operation.
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.
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.
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.
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
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.
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.
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.
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.
Due to the global development of the industry and technology in the 20th century, increased production of vehicles and the growing population resulted in massive consumption of fossil fuels. Today we face three challenges regarding environmental and energy issues, which are finding an alternative energy source as opposed to oil, reducing CO2 emissions, and preventing air pollution.
Although the demand for oil alternatives, such as gas fuels, electricity, and hydrogen may grow, each alternative energy source has its disadvantages. Oil is currently the main source of automotive fuel, but further research and development of alternative energy in the future may bring change. Various powertrains, such as those found in Plug in Hybrid vehicles, electric vehicles and fuel cell vehicles, will be required in order to use diversified types of fuels.
At Toyota, we will continue to develop various vehicles, along with our emphasis of conventional vehicles and hybrid vehicles as fundamental core technology while pursuing further advancement. Based on these core technologies, Toyota will develop next-generation vehicles utilizing alternative fuels such as gas fuel, electricity and hydrogen.
Electricity, hydrogen, biodiesel and natural gas are good alternatives for fossil fuel, but each source has their own disadvantages. The left figure shows compares the energy density of each alternative fuel.
Even with the latest lithium ion battery technology, only 1/50 of the energy required by gasoline is used. Although powering a motor with electricity is much more efficient than an internal combustion engine, liquid fuels such as gasoline are still advantageous because of their high volume in energy density. The figure below shows the difference in energy density between electricity and gasoline but does not indicate correlation in cruising range.
The cost of batteries also poses a major challenge. In an effort to attain the 2030 Innovative Technology Plan issued by Japan's Ministry of Economy, Trade and Industry, we have barely reached the status to be at a competitive level with gasoline powered vehicles.
For more improvements in efficiency, Toyota proactively manages powertrain efficiency, reduces vehicle load, and controls energy management by integration of fuel-saving technologies such as charge control, idling stop, etc.
Toyota has a long history of continuous improvement when it comes to conventional engines, including lean-burn gasoline engines, direct injection gasoline 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 (for Electric Vehicle).
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. We develop these key technologies in-house to reduce costs and rapidly commercialize their application.