Toyota Prius Paves The Way Ahead | Part Two

Performance, Economy And Low Emissions

The new Toyota Prius can return a fuel consumption that is comparable to the best B-segment diesels. Production of CO2 and NOx is also radically low, while particulate matter emissions are non-existent. Figures for consumption are 65.7mpg for combined and 67.3mpg for extra-urban driving. In the urban cycle, Prius returns 56.5mpg, which beats every B-segment car on the market by a large margin. At the same time, this D-segment car can accelerate from nought to 62mph in less than 11 seconds.

The new Prius largely surpasses EURO IV emission standards. Hydrocarbon and nitrogen oxides emissions are respectively 80 and 87.5 per cent lower than required by EURO IV regulations for petrol engines. Furthermore, at a time when most diesel engines on the market don’t even comply with EURO IV, Prius NOx emissions are 96 per cent below the EURO IV level for diesel cars. In addition, Prius produces only 104g/km of CO2 exhaust emissions (on the combined cycle), and breaks the 100g/km barrier on the extra-urban cycle (99g/km).

The new hybrid system, making its debut in the Toyota Prius, is the first to be developed according to a revolutionary concept, Hybrid Synergy Drive. Current generation hybrids rely on the petrol engine to produce peak performance, with the electric motor as an ancillary. Toyota Hybrid Synergy Drive gives the electric motor a more significant role and also focuses on stronger performance.

A more powerful 1.5-litre petrol engine works together with the smaller, more efficient electric motor to deliver performance that positions the Prius as a serious contender in the D-segment. The electric motor is now more powerful than most 1.0 to 1.2-litre internal combustion engines and, at 400Nm from nought to 1,200rpm, the Prius’s torque surpasses that of modern V6 diesels. As a result, nought to 62mph is accomplished in less than 11 seconds, making Prius almost three seconds faster than the first generation model and comparable to a conventional 2.0-litre diesel engine.

Regenerative Braking System

In a conventional car, each time the brakes are applied to slow down, kinetic energy is wasted. Not so in the Prius, as this energy is captured and fed back into the battery as electrical energy to keep the battery fully charged. This is particularly useful during city stop-start driving.

Under braking the electric motor operates as a generator converting the vehicle’s kinetic energy into electricity, which is used to keep the battery fully charged. Each time the footbrake is applied the system controls the coordination between the hydraulic brake, the Electronically Controlled Brake System (ECB) and the regenerative brake to preferentially use regenerative braking, thereby recovering energy even at very low vehicle speeds. ECB (a brake-by-wire system) also brings a huge improvement in terms of regenerative braking performance.

continues... | Part Three
Published 3 December 2003 Melanie Carter

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