The littlest Toyota, the Yaris, is about to become hybridized too, and the engineering job to reduce the size of its Hybrid Synergy Drive system for the diminutive car is worth a look. The hybrid engines from the larger Toyotas such as the Prius and Auris were too large for the Yaris as they would have eaten into passenger space, and as the car's catchcry promotes a "small outside, big inside" character, a new powerplant was prescribed.

Toyota was obviously very keen to bring hybrid drive to the tiny Yaris, which is sold as the Vitz in some markets and the Diahatsu Charade in others.

The size of the motor has been reduced by 20 per cent and thePCU12 per cent, compared to those in Auris Hybrid; and the trans-axle has shed 11kg and is six per cent shorter.

The system uses a new 1.5-litre Atkinson cycle petrol engine that weighs 16.5kg less and is 10 per cent more compact than the 1.8-litre unit used in the Prius and Auris.

Likewise, other major components such as the electric motor, power control unit and trans-axle were also made lighter and smaller, but the power has remained robust at 99 bhp (74 kW)

The packaging challenge also demanded careful thought about the size and location of the nickel-metal hydride battery pack and the fuel tank, in order to minimize the impact on cabin space for rear seat passengers and the size of the boot. Both are positioned under the rear bench seat, which means the car's load space capacity, and rear passenger space is unaffected.

There have been no emission figures announced for the new power train yet, though the press release was carefully worded, claiming the Yaris hybrid would deliver "class-leading CO2, NOx and particulates emissions, together with excellent fuel consumption."

Most importantly, the hybrid Yaris will go on sale mid-year with very low fuel consumption, emissions, and ownership costs.