low carbon cars

The Prius has been called a true hybrid vehicle, designed from the bottom up. Toyota's goal for the Prius was to reduce the amount of pollutants it produced and to be as energy-efficient as possible. They used several methods to try to achieve this goal, including:

More efficient use of the internal combustion engine (ICE), reducing petrol consumption. The 1NZ-FXE engine uses the more efficient Atkinson cycle instead of the more common Otto cycle;
Two electric motor/generators, providing 50 kW (67 hp) @ 1,200 to 1,540 rpm and 400 N·m (295 ft·lbf) torque from 0 to 1,200 rpm, which significantly contribute to performance & economy;
50 kW IGBT inverter controlled by a 32-bit microprocessor, which efficiently converts power between the batteries and the motor/generators.
Lower coefficient of drag at 0.26 (0.29 for 2000 model), reducing air resistance, especially at higher speeds;
Lower rolling-resistance tyres on the prius, reducing road friction;
Regenerative braking, a process for recovering kinetic energy when braking or traveling down a slope and storing it as electrical energy in the traction battery for later use while reducing wear and tear on the brake pads;
Sealed 168-cell nickel metal hydride (NiMH) battery providing 201.6 volts;
Continuously variable transmission — the Prius does not use a typical CVT; Toyota calls it the Power Split Device. The electric motors and petrol engine are connected to a planetary gear set which is always engaged, and there is no shifting.
Flexible resin petrol tank, reducing the amount of hydrocarbon emissions in the form of escaped petrol vapour;
Vacuum flask coolant storage system that stores hot engine coolant, then reuses it to reduce warm-up time.
Weight reduction — for example the bonnet and boot are made of aluminium instead of steel.
Touted advantages of the Prius over previous energy-efficient designs include never needing to be plugged in, as all energy ultimately comes from the gasoline engine. This means it drives like a traditional ICE car, with the onboard computer taking care of shifting power to and from the engine and motors, and automatically determining when to charge the battery, as well as the most efficient use of the engine or the electric motors (or both) based on driving conditions. This also means that one cannot use electricity from external sources; some consider this to be a serious disadvantage. The Prius recovers energy that would be otherwise wasted: when braking, the car's kinetic energy is partly recovered to recharge the battery instead of being wasted as heat. This also reduces brake wear.


Electric power steering. The engine can shut down once it has warmed up and the catalytic converter in the exhaust system has reached operating temperature. The Prius can then be driven on electric power only; this is sometimes referred to as "stealth mode" due to the lack of engine noise. This further reduces gasoline consumption and wear and tear on the engine. When driving conditions demand additional power from the engine, it starts up automatically.


A battery module used on the Prius. The on-board computer ensures that the engine runs under the most efficient conditions. Typically, a gasoline engine runs inefficiently when throttle is half-open, creating a choking operation conditions. This effect, called pumping loss, is a major reason for the inefficiency of gasoline engines compared to diesel engines. The Prius minimizes the pumping loss by running the petrol engine at high torque range with throttle fully open. Drive-by-wire technology and CVT are essential in this engine control.


Energy Monitor on the Prius Multi-Function Display, showing energy flow to/from the engine, battery, and from the regenerative braking, as well as battery charge level.As well as the immediate benefit of reducing fuel consumption and emissions, stopping the engine also improves the performance of the catalytic converter, as in a normal vehicle the exhaust gases from an idling engine tend to cool the catalysts below their optimal temperature.


Energy screen on the Prius unlike in conventional cars, frequent starting up and shutting down of the engine causes neither additional wear and tear nor emission problems, because the drive motors have enough power to quickly and smoothly spin the engine to optimal rpm (around 1,000) before the engine actually begins to "fire up". This avoids wear when the engine is "running" (with fuel and spark) at very low rpm, as happens in most vehicles.

For any car, aerodynamic losses due to drag are much greater on the motorway than in low speed urban driving. A non-hybrid car nonetheless gets worse mileage in urban driving because its engine is far less efficient at low power, such as when stopped in traffic, and because it must frequently dump its kinetic energy into the brakes during stop-and-go driving. The Prius occasionally gets better fuel efficiency in the city because the engine can shut down instead of running at low power, and run solely off the battery at low speeds and when stopped. Also, the car's kinetic energy can be captured when braking, and stored in the battery. According to EPA tests the 2004-2006 Prius gets 65 mpg in the city, compared with 55mpg on the motorway and Natural Resources Canada estimates 58.8 mpg in the city and 56mpg on the motorway. This means the greatest advantages of a hybrid are mainly in city driving such as minicabs and taxis. The hybrid has less of an advantage in high speed driving, but it can still use a smaller and more efficient engine than would otherwise be required because the battery and electric motor can provide the extra peak power needed for passing and hill climbing.
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