Multiair

MultiAir is a term used by Fiat for an electro-hydraulic control system for flexible inlet valve timing in gasoline engines. The system was developed by Fiat Powertrain Technologies along with the Schaeffler Group and is produced by Schaeffler. The UniAir valve control system made ​​its debut in the Alfa MiTo 1.4 MultiAir.

Function

The system acts on the intake valves, the outlets are as usual operated by the camshaft. Between the camshaft and intake valves for each cylinder is a system with roller cam and a hydraulic piston with encoder, pressure chamber, solenoid valve and slave piston on the intake valves. The solenoid valve is open, the oil in the pressure chamber can take place in a low-pressure circuit; the respective intake valves close early. The solenoid valve remains closed, however, the oil can not flow. Therefore, in the chamber pressure builds up, causing the following affiliated intake valves the cam. This is also called "lost motion" because the system the valve can only decrease. The valves are closed as usual by springs. The low pressure system fills the pressure chamber during the other cycles and acts as a hydraulic valve play compensation.

When the solenoid valve during the intake stroke is first opened and then closed again, it can be possible to open the intake valve more than once.

Effects

By the direct intake control the cylinder charge can be controlled, without requiring a throttle valve must be operated. The throttle valve is only needed for emergency following the failure of the system and always open during normal operation.