Multiair Fiat Valve-Lift System Explained. Surging gas prices and impending regulations are causing automakers to hunt for ways to increase the efficiency of gasoline engines. One of the chief inefficiencies of these engines is the restriction that’s created by the throttle plate in the intake passage, which is used to regulate how much air feeds the cylinders. Referred to as “pumping losses,” this bottleneck caused by a partially open throttle forces an engine to squander about 10 percent of energy that could otherwise be used for propulsion.
BMW, Nissan/Infiniti, and Fiat have overcome much of these pumping losses by instead throttling their engines via the intake valves—varying their lift and the amount of time the valves are open to control the engine. BMW was first, with its Valvetronic technology, which was launched on various models in 2001. It’s a complex system that uses an additional electronically actuated camshaft to vary valve lift.
The beauty of Fiat’s “Multiair” system is its simplicity; it essentially achieves what Valvetronic does by using hydraulic fluid running through narrow passages connecting the intake valves and the camshaft so the two can be decoupled. This system is modulated by an electronically controlled solenoid, and there are effectively two modes: When the solenoid is closed, the incompressible hydraulic fluid transmits the intake-cam lobe’s motion to the valve, as in a traditional engine. When the solenoid is open, the oil bypasses the passage, decoupling the valve, which then closes conventionally via spring pressure. For example, to shut the valves early, as in a part-load situation, the solenoid would be closed initially and then open partway through the intake cycle. The tricky business is correctly timing the switching of the solenoid, and Fiat has painstakingly optimized the responsiveness of the electronic controls. Aside from the fuel-economy and emissions benefits, Fiat claims Multiair can also enable a 10-percent horsepower boost. This technology will go into production in Europe later this year on a 1.4-liter turbo and will also be used on naturally aspirated engines as it spreads throughout Fiat’s lineup.
The beauty of Fiat’s “Multiair” system is its simplicity; it essentially achieves what Valvetronic does by using hydraulic fluid running through narrow passages connecting the intake valves and the camshaft so the two can be decoupled. This system is modulated by an electronically controlled solenoid, and there are effectively two modes: When the solenoid is closed, the incompressible hydraulic fluid transmits the intake-cam lobe’s motion to the valve, as in a traditional engine. When the solenoid is open, the oil bypasses the passage, decoupling the valve, which then closes conventionally via spring pressure. For example, to shut the valves early, as in a part-load situation, the solenoid would be closed initially and then open partway through the intake cycle. The tricky business is correctly timing the switching of the solenoid, and Fiat has painstakingly optimized the responsiveness of the electronic controls. Aside from the fuel-economy and emissions benefits, Fiat claims Multiair can also enable a 10-percent horsepower boost. This technology will go into production in Europe later this year on a 1.4-liter turbo and will also be used on naturally aspirated engines as it spreads throughout Fiat’s lineup.
