Toyota hybrid cars

Toyota was the first company to mass-produce a hybrid vehicle. The Prius went on sale in Japan in 1997 and was subsequently introduced worldwide in 2001. Overall from August 1997 to February 2011 Toyota Motor Corporation has sold more than 3 million hybrid cars. Today Toyota-produced hybrids make up approximately 75% of United States hybrid sales.

Hybrid Synergy Drive

Toyota uses Hybrid Synergy Drive (HSD) technology to produce full hybrid vehicles. HSD replaces the gear box (transmission), alternator and starter motor with a pair of powerful motor-generators with a computerized shunt system to control them, a mechanical power splitter that acts as a second differential, and a battery pack that serves as an energy reservoir. Motor generator 1 generates electrical power to recharge the high voltage (EV) battery and supplies electrical power to drive MG2, it also serves as the engine starter. Motor generator 2 drives the car (together with the combustion engine) and during regenerative braking converts kinetic energy into electrical energy, which is then stored in the EV battery.

The motor-generator uses power from the battery pack to propel the vehicle at startup and at low speeds or under acceleration. The internal combustion engine (ICE) may or may not be running at startup. When higher speeds, faster acceleration or more power for charging the batteries is needed, the ICE is started by the motor-generator (acting as a starter). These features allow the ICE to normally be turned off for traffic stops.

When a driver wants the car to slow down, the initial travel of the brake pedal engages the motor-generator into generator mode converting much of the forward motion into electrical current flow which is used to recharge the batteries while slowing down the vehicle. In this way the forward momentum regenerates (or converts) much of the energy used to accelerate the vehicle back into stored electrical energy. This process is called regenerative braking. Harder braking action engages standard brakes which are also provided for faster stops and emergency use.

The mechanical gearing design of the system allows the mechanical power from the internal combustion engine (ICE) to be split three ways: extra torque at the wheels (under constant rotation speed), extra rotation speed at the wheels (under constant torque), and power for an electric generator. A computer program running appropriate actuators controls the systems and directs the power flow from the different engine and motor sources. This power split achieves the benefits of a continuously variable transmission (CVT), except that the torque/speed conversion uses an electric motor rather than a direct mechanical gear train connection. There is no reverse gear as in a conventional gearbox: the computer feeds negative voltage to motor generator 2, applying only electric negative torque to the wheels.

The Atkinson internal cycle combustion engine itself was also designed specifically to minimize engine drag via an offset crankshaft to minimize piston drag during the power stroke, and a unique intake system to prevent drag caused by manifold vacuum versus the normal Otto cycle in most engines. Furthermore, the Atkinson cycle recovers more energy per cycle than the Otto because of its longer power stroke. The downside of the Atkinson cycle is much reduced torque, particularly at low speed; but the HSD has enormous low-speed torque available from the motor generator.

Toyota hybrid models