The Prius shows an extraordinary commitment to a new technology from a major manufacturer, Toyota. There seems little doubt that it was the personal conviction of Dr Shoichiro Toyoda, president of the company, that drove this, for he is on record as stating, some time before such views became commonplace, that CO2 emissions and global warming were the greatest problems facing mankind.
The hybrid-drive Prius uses a petrol (gasoline) engine plus two electric motors/generators and a substantial battery pack to allow it to run with electrical or engine power, or any proportion of both. Efficiency advantages come from the fact that the petrol engine only drives the road wheels via the electrical system and therefore always runs at its most efficient speed and power setting. Thus it never needs to run inefficiently at low speed or small throttle openings. Moreover, under deceleration the motors then function as dynamos, recovering kinetic energy and producing electrical power to charge the batteries. The efficiency of this set-up is a matter of ongoing debate.
The Prius performs well for fuel economy, but some users and reviewers suggest that a simple and efficient diesel engine will beat the more complex Prius on both consumption and on emissions, particularly when whole-life ‘cradle to grave’ build and disposal costs are compared. However, hybrid technology is new and constantly improving.
There is no doubt that the Prius is a technological tour de force, though its great success in locations such as London and California has been helped by favourable tax or charging regimes.
The hybrid petrol–electric power plant is one route to an efficient car with low emissions. Toyota has made a brave and committed move to this new architecture.