The only other brand that today has something similar in their gasoline engines. This is BMW (and Mini) and fully open system Valvetronic variable intake valves, in this case driven by the camshaft and without butterfly, which works with the same engine lubricating oil, ie, reliability maximum and applied to atmospheric and turbocharged engines with direct injection. Multiair system logo at the top nice engine, the only place where it appears.

According to Fiat, compared with a conventional gasoline engine of equal size, offers more power (up to 12%) and torque (up to 15%), while consumption is lower (up to 16%), with lower CO2 emissions (up to 16%), and fewer particles (up to 40%). It even allows internal recirculation of exhaust gases through the reopening of the intake valves during the exhaust, causing a reduction in emissions of 40% of HC / CO and 60% of NOx.

All an invention, with a high development potential ahead by ensuring the reliability (Fiat patent is put into production but is Bosch) and also apply to diesel engines. The difference is remarkable about the old 1.4 turbo 120 hp with conventional admission, which approved 6.6 l/100 km and 155 g / km respectively, although some of this reduction is attributable to the start & stop system.

Multiair system (press file)

The operating principle of the system applied to the intake valves is as follows: a piston driven by a mechanical cam (1), is connected to the inlet valve by a hydraulic chamber controlled by a solenoid valve, the ON / OFF, normally open.

Drawing of the multilateral system of Fiat in red are the two exhaust cams camshaft for a cylinder and then green, the 3rd cam to activate the system Multiair admission. The four equal sets consisting of the Multi (one per cylinder) should be considerably more expensive than a traditional intake system with camshaft and reliability, necessarily smaller. View of the 3 rd cam that drives the system Multi from the other end of the exhaust camshaft and from the same side of the engine.

When the valve is closed, oil in the hydraulic chamber behaves like a solid body and transmitted to the intake valves appellate law imposed by mechanical suction cam. When the valve is open, the hydraulic chamber and the intake valves are separated and do not follow the intake cam, closing due to the spring force. The final part of closing, the valve is controlled by a specific damping, which ensures a smooth closing and regularly in all operating conditions.

Controlling the opening and closing moments of the solenoid valve can easily obtain different optimal performances opening the intake valves. For maximum power, the solenoid valve is always closed and the full opening of the valves is carried out in completely the evolution of mechanical cam that has been optimized specifically for power at high speeds (extended closing times).

At low speed and full load, the solenoid valve opens near the tip of the cam profile, making an early closure of the valve admission. This eliminates unwanted reflux in the collector and maximizes the enclosed air mass in the cylinders.

In partial load conditions of the engine, the solenoid valve opens early (before completing the mechanical cam profile) performing a partial opening of the valves to control the air mass introduced by the torque. It is also possible to obtain a partial opening of the valves, solenoid valve closed once it started the mechanical cam. In this case, the flow of air entering the cylinder has a top speed and generates a particularly high level of turbulence in the cylinders.

You can combine these two modes of action for the same event of aspiration, with the mode called “Multilift, which increases turbulence and burning rate regimes and very low loads.