Multiair (or Uniair) is an electro-hydraulic variable valve actuation technology controlling air intake (without a throttle valve) in gasoline engines. It is compatible with both naturally aspirated and forced-induction engines.
Multiair technology was patented by Fiat in 2002; it was launched at the 2009 Geneva Motor Show to be available in the Alfa Romeo MiTo. Production of the new engine started in Termoli, Italy at the Fiat Powertrain Technologies factory. The 1.4 L Multiair engine won the "Best New Engine of 2010" award. For the Fiat 500 North American version the 1.4 L engine is produced also at the Global Engine Manufacturing Alliance in Dundee, Michigan, United States. The MultiAir valvetrain components for the North American market Fiat FIRE and Chrysler Tigershark engines are manufactured and assembled by Schaeffler Group in Cheraw, South Carolina. The Fiat TwinAir 875 cc two-cylinder engine is also using Multiair technology, it was named as Best New Engine of 2011.
The basic idea, controlling intake valves, works upon the following principle: a valve tappet (cam follower), moved by a mechanical intake cam, is connected to the intake valve through a hydraulic chamber, controlled by a normally open on/off solenoid valve. The system allows optimum intake valve opening schedules. An example of the gains offered by the MultiAir technology can be seen in the current Alfa Romeo MiTo: the 1.4 TB engine, without MultiAir, can produce 155 PS (114 kW; 153 hp) and 230 N·m (170 lb·ft) whilst using 6.5 litres per 100 kilometres (43 mpg-imp; 36 mpg-US). With MultiAir, the same engine develops 170 PS (125 kW; 168 hp) and 250 N·m (180 lb·ft), yet only consumes 6.0 L/100 km (47 mpg-imp; 39 mpg-US). MultiAir engines will increase power (up to 10%) and torque (up to 15%), as well as considerably reduce consumption levels (up to 10%) and emissions of CO2 (up to 10%), particulates (up to 40%) and NOx (up to 60%) when compared to a traditional petrol engine. The system also provides smoother cold weather operation, more even torque delivery and no engine shake at shut-off. The Multiair technology took over a decade to develop. The vice president of Fiat Powertrain Research & Development Rinaldo Rinolfi led the team who developed the technology. Development costs were over $100 million. There was also a delay in its development, at a time (2000-2005) when Fiat was in partnership with General Motors.
More advanced, fully camless valvetrain systems are under development, but are not yet production-ready. The Valvetronic system used by BMW allows the valve timing and lift to be varied but not the cam profile. The ability to vary the latter is characteristic of camless and the Multiair systems.
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