Multiair

from Wikipedia, the free encyclopedia
Fiat Multiair 1.4 turbo engine

MultiAir is a Fiat name for an electro-hydraulic control system for flexible inlet valve control in gasoline engines . The system was developed by Fiat Powertrain Technologies together with the Schaeffler Group and is produced by Schaeffler. The UniAir valve control system debuted in the Alfa MiTo 1.4 MultiAir in 2009 .

Uniair is the fundamental technology created by Fiat's research that Multiair introduced for the time being only for intake valves.

function

In the Multiair cylinder head there is an overhead camshaft which , as usual, mechanically actuates the exhaust valves with the exhaust cams via bucket tappets . There is one inlet cam per cylinder on the camshaft. This does not act directly on the inlet valves, but on an electro-hydraulic transmission unit, which consists of a roller rocker arm and a hydraulic system with a master piston, pressure chamber, solenoid valve and slave piston on the two inlet valves. The lift of the cam is transmitted to the intake valve stems by the oil hydraulics. If the solenoid valve arranged in the pressure chamber remains closed during a valve stroke, no oil can flow out and the valves follow the elevation curve specified by the cam shape. If, on the other hand, the solenoid valve is opened by the engine control unit , part of the oil can escape from the pressure chamber into a low-pressure circuit; the respective inlet valves open shorter and less than specified by the cam or not at all. This means that both the valve lift and the times of valve opening and closing (i.e. the inlet control time) can be variably controlled by the electrical control of the solenoid valve - within the limits specified by the mechanical shape of the cam. One also speaks of a “lost motion system” because the electronics and hydraulics can only reduce the valve lift that is dictated by the cam shape. The valves are closed by springs as usual . The low pressure system fills the pressure chamber during the other cycles and acts like a hydraulic valve clearance compensation.

If the solenoid valve is opened several times during an intake stroke (and thus in the pressure build-up phase by the cam) and then closed again, the inlet valve can also be opened several times - each with a smaller stroke.

Effects

Thanks to the variable intake control, the cylinder charge can be regulated directly without a throttle valve . The conventional throttle valve that is still present is only required for emergency operation after the system fails and is always fully open in normal operation. This reduces the throttling losses in the intake tract, which benefits fuel consumption. An improvement in engine performance and efficiency is to be achieved by adapting the valve lifts and control times depending on the load and speed. The starting and cold start behavior of the engine should also be improved.

Web links

Individual evidence

  1. ↑ Jörg Walz: PACE Award for consumption-reducing innovation. Schaeffler receives PACE Award for UniAir and Innovation Partnership Award for successful cooperation with Fiat. In: press release. Schaeffler AG, May 7, 2012, archived from the original ; accessed on November 7, 2016 : "The UniAir valve control system developed jointly by Fiat Powertrain and Schaeffler and industrialized by Schaeffler celebrated its premiere in 2009 in the Alfa MiTo 1.4 MultiAir."
  2. ↑ National Academy of Sciences (Ed.): Assessment of Fuel Economy Technologies for Light-Duty Vehicles . National Academies Press, Washington 2011, ISBN 978-0-309-15607-3 , Electro-hydraulic CVVL Systems, pp. 4 · 13 ( Online , Google Books ).
  3. ↑ a b c d First fully variable electro-hydraulic valve control Uni Air / MultiAir. Kfz-Technik Wiesinger, accessed on November 7, 2016 .