Fiat's 'Multiair' system

MultiAir is a hydraulically-actuated variable valve timing and variable valve lift engine technology enabling "cylinder by cylinder, stroke by stroke"control of intake air directly via a gasoline engine's inlet valves. Developed by Fiat Powertrain Technologies, the technology bypasses a primary engine inefficiency: pumping losses caused by restriction of the intake passage by the throttle plate, used to regulate air feeding the cylinders.

MultiAir was licensed to the Schaeffler Group in 2001, which also markets the system as Unfair.Schaeffler began supplying Uniair systems in 2017 to Jaguar Land Rover, branded as Ingenious technology.

Fiat S.p.A., now FCA, launched MultiAir in 2009 employing a proprietary electro-hydraulic system to precisely control air intake without a throttle valve, in order to increase engine power and torque, reduce fuel consumption, reduce emissions — and improve engine operation — offering "a more controllable flow of air during the combustion cycle in comparison with mechanical VVT systems."The technology allows engines to be lighter and smaller while reducing pumping losses — and can be adapted to existing engines by replacing the camshaft with the MultiAir system, thus requiring a new head only.

Compatible with both naturally aspirated and forced-induction engines, MultiAir technology was patented by Fiat in 2002 and was launched at the 2009 Geneva Motor Show in the Alfa Romeo MiTo. Launched in Fiat's FIRE 1.4 units, e.g., in the Fiat 500²⁰⁰⁷, 1.4 MultiAir engines for global markets are manufactured in Tremolo, Italy at the Fiat Powertrain Technologies factory and at the FCA's Dundee Engine Plant (formerly of Global Engine Alliance's GEMA manufacturing branch), with critical systems manufactured and assembled by Schaeffler Group.

In 2010, the 1.4L MultiAir engine won the International Engine of the Year as well as Popular Science's Best of What's New.In the same year, the Fiat SGE engine (0.9 turbocharged and 1.0 naturally aspirated TwinAir units), also using MultiAir technology, was launched in the Fiat 500. It is produced in Niels ko-Biała, Poland. It was named Best New Engine of 2011.

Both FIRE and SGE units equipped with MultiAir use indirect fuel injection.

MultiAir II, using direct fuel injection, was made available in the GME (Hurricane) and GSE (FireFly) units, starting from 2016.

How it works

"The MultiAir system is elegantly simple. An electrohydraulic actuator—a high-response, electronically activated solenoid—controls the pressure applied to hydraulic fluid (engine oil drawn from the sump) that fills a thin passageway that connects the intake valves and the camshaft. The solenoid valve regulates the amount of oil that is pumped by the cam action either to the valve or a bypass reservoir.

When pressurized, the hydraulic line behaves like a solid body and transmits the lift schedule imparted by intake cam directly to the intake valve. When the solenoid is disengaged a spring takes over valve actuation duties.

This electrohydraulic link allows independent operation of the two components, which enables near real-time control over the valve lift profiles, said Bernard. Whereas a closed solenoid transmits the pressure generated by the camshaft’s intake profile to the valve in the normal fashion, an open solenoid breaks the hydraulic link between cam and valve, decoupling their operations."