The main source of power for Toyota's hybrids remains the gasoline engine. But these aren't your ordinary powertrains. They're built for high efficiency and low emissions. The Prius and Camry hybrids work off a four-cylinder, high expansion ratio Atkinson cycle engine. Atkinson cycle engines squeeze optimum energy from gasoline combustion by increasing the expansion ratio and by extracting every last bit of power from the gas-air mix. For more power, the Highlander Hybrid features a V6 Otto cycle engine, which increases efficiency by compressing the fuel mixture before ignition.
Electric Drive Motor
A result of Toyota home-grown technologies and work done on pure electric vehicles, the Electric Drive Motor is an AC synchronous-type motor using permanent neodymium magnets and a rotor consisting of stacked electromagnetic steel plates. Because the magnets are arranged in an optimal V-shape configuration, the motor produces both high output and drive torque.
Power Control Unit
The Power Control Unit is the brains behind the hybrid system, integrating gas engine and electric motor power in a way that is both seamless and achieves the highest levels of performance. The unit contains an inverter to convert direct current from the battery to alternating current to run the electric motor, and a DC/DC converter to produce 12V current. As well, the unit's high-voltage power circuit raises the voltage from the power supply, thus allowing a reduction in current and subsequently a reduction in the size of the inverter. More power. Less space.
High Voltage Battery
The Toyota hybrid nickel-metal hydride HV battery never needs to be plugged in. That's because the battery is being constantly re-charged by either the gas engine by way of the generator when in cruising mode, or by the electric motor during deceleration and regenerative braking. And the latest battery has been further enhanced through improved electrode material and a new connection structure between battery cells. Tests show that the battery maintains efficiency for up to 300,000 km without deteriorating.
The AC synchronous-type generator is just the thing to charge the battery and supply power to the high-output electric drive motor (or motors, in the case of the Highlander Hybrid) as needed. To provide the optimum power to the motor, the generator is rotated at high speeds, thus increasing the rpm range from the conventional maximum output of 6,500 up to a whopping 10,000 rpm. A higher rpm rate increases power supply in the medium-speed area and improves acceleration in the low/medium-speed range. The result is more power when you need it without burning extra fuel.
Planetary Gear (Power Split Device)
By splitting power into two routes: mechanical and electrical, the planetary gear, also known as the "hybrid transaxle," can transfer power between the engine, motor/generator, and wheels in just about any combination you could imagine. Directly linked to the engine, the rotational shaft of the planetary carrier inside the gear mechanism is able to transmit the motive power to the outer ring gear and the inner sun gear, using pinion gears. The rotational shaft of the ring gear, on the other hand, is directly linked to the motor. It transmits the drive force to the wheels, while the rotational shaft of the sun gear is directly linked to the generator. Talk about getting in gear.
When starting up, stopped at intersections and lights, or moving at low speeds, the car is powered solely by the electric drive motor, drawing energy from the hybrid battery through the power control unit. Not only does this save on fuel and result in zero emissions, but the electric drive motor also helps the acceleration process by delivering maximum torque instantly. Call it a win-win situation.
When the car needs to accelerate quickly, to pass another car on the highway, for example, the engine and electric drive motor team up to supply power for smooth and powerful acceleration. The hybrid battery does its bit by providing the extra energy needed to increase drive power. The combination of direct mechanical power from the engine and electric power from the motor, together with the Electronically Controlled Continuously Variable Transmission (ECVT), deliver responsive acceleration when you most need it.
When cruising and under normal driving conditions, both the gasoline engine and electric motor supply power to the wheels. At higher speeds, the gasoline engine does most of the work and the electric drive motor kicks in when needed; at lower speeds, it's the other way around. Engine power is divided between the wheels and the generator for maximum efficiency by way of the planetary gear. The generator drives the electric motor and also helps recharge the hybrid battery from surplus engine power. That's why it's called a Hybrid Synergy Drive system: it all works smoothly together for amazing results.
For most cars, braking means loss of energy through heat and friction. But, when you take your foot off the accelerator or apply the brakes on a Toyota hybrid car, you actually help recharge the battery and boost system efficiency. Thanks to a regenerative braking system, kinetic energy from the wheels is transformed into electricity and sent by the electric motor to the power control unit - and then stored in the hybrid battery. In other words, the electric motor becomes a generator, driven by the car's wheels. This system is especially effective in the stop-and-go of urban driving. Re-usable energy - now there's a concept.
When you put a hybrid car into reverse, under normal circumstances only the electric drive motor will be in operation. That's because the power control unit shuts down the gasoline engine when it isn't needed - at low speeds or when coasting. In fact, the only time the gasoline engine will come on when in reverse is to charge the hybrid battery.