Car reviews - Toyota - Prius - i-Tech 5-dr hatch
9 Jul 2004
The Prius engine is also seen, in slightly different form, in the Toyota Echo. The direct-injection, long-stroke, all-alloy, twin-camshaft, 16-valve 1.5-litre engine incorporates variable valve timing and produces 57W at a low 5000rpm, and 115Nm of torque at 4000rpm. This is better than seven per cent more powerful than before, and it spins just a little harder to do it. Improvements include lighter pistons, reduced friction, smaller size and reduced weight – down to 84kg. It also gets an electronic throttle, a new 32-bit electronic control unit (previously 16-bit) and faster communication between the control systems - engine electrical, chassis electrical and the hybrid system. There are new, lighter, re-shaped pistons and lighter exhaust manifolds that help reduce light-up time for the catalytic converter. Where it differs from the Echo engine is in the use of the high-expansion ratio "Atkinson" cycle rather than the more familiar "Otto" cycle in which expansion and compression strokes are virtually identical. In the Prius, the exhaust valves remain closed for the complete expansion stroke, maximising torque. However, on the compression stroke the intake valves initially stay open, which has the effect of lowering the compression ratio – even though the small combustion chamber still produces a high 13.0:1 compression. The system is similar to the Miller cycle seen on the supercharged engine used in the Mazda Millenia-Eunos 500 except that it is coupled – for the first time, Toyota says – to a normally aspirated engine. There’s also a new radiator, and an improved fuel delivery system via aluminium main fuel and purge tubes.
Did you know?Prius II aims to meet California’s strict new AT-PZEV emission regulations, Japan’s Ultra-Low Emission Levels and Euro IV regulations. Toyota says the Prius satisfies California’s Advanced Technology Partial Zero Emission Vehicle regulations scheduled for January 2005
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