How does the multiair "MULTIAIR® Fiat" works

Within the coming years the new Fiat MULTIAIR® thrusters that promise consumption and emissions record. Here's how it whorks

The waiting was long but at the Geneva Motor Show has finally been officially presented the new technology MULTIAIR®, which will debut on Alfa Romeo Mito in 2009. To confirm the news was Alfredo Altavilla, CEO of Fiat Powertrain.

The MULTIAIR® is the proposal of Fiat for the valve control system, with which you can save up to 25% in consumption, an increase similar in terms of torque and power delivered by the engine.

In gasoline engines, the power is modulated by the throttle valve, a disk controlled by a pedal that controls the passage of air into intake. The amount of air and gas released into the engine, must be in a ratio of 14:1 (the stoichiometric ratio), thus controlling the amount of air is also controls the gas released, with the result of managing the power output from the engine.

The use of the throttle valve it make losing energy to the engine, increasing consumption and emissions when the valve is slightly open, then in that condition requires little power to the engine as is typical in the city. Similarly, adjusting the valve corresponds to a person drinking from a straw regulates the amount of water that wants to drink by crushing the straw. The result is a greater effort, resulting in wasted energy.

The solution to this problem is to control the air sucked from the engine, changing the timing opening of the intake valves of the engine. Intelligent solution, but extremely complex to implement.

In most four-stroke engines, the valves were fixed opening profiles obtained through a rotating cam that pushes the valve or move on with the rocker shaft. Over time have been proposed alternative solutions to operate the valve, through an electric motor (BMW Valvetronic, for example), with a hydraulic piston or electricomagnetic.

All these solutions are never able to succeed on a large scale for various reasons such as cost and space, or because you're never able to obtain solutions that are reliable.

The solution developed by Fiat with the MULTIAIR®i is a combination of a system without a camshaft and hydraulic control valves. To understand the operation is useful to refer to the insight of the system, in which the cam actuates a hydraulic piston that in turn controls the intake valve.

The oil is practically incompressible and thus acts as a rigid object and therefore the system is identical to a classic operation of the valves. The trick is in a valve ON / OFF switch that opens the room that contains the oil, putting it in communication with a small reservoir positioned next to it. When this valve is opened, the oil put under pressure by the cam goes into the tank and pushes the cam, which will be closed by a spring.

To obtain a delayed just close the valve ON / OFF with a slight delay, and to close early is simply open the valve in advance. Managing the timing of valve opening, it adjusts the airflow to the engine regardless of the throttle

Theoretically MULTIAIR® engines do not need the throttle, but in reality, the throttle is still present but is now electro-implemented, and is no longer managed by the driver via the accelerator pedal.

In the information issued by Fiat are not present the details related to this choice, probably linked to security reasons in case of malfunction. In reality there is another aspect of interest, which is one of the difficulties that FPT engineers have faced in the design of MULTIAIR®, or the inability to measure and then know the position of the valve reached.

The system allows you to choose when to send the command to open or close the valve, but you can not know exactly when this will happen, nor can it be measured in the position to reach the valve. If that were the case might have been completely eliminate the fafalla. This is emphasized when one considers that the compressibility of oil varies with temperature, which affects the delay between the command and the actual opening. This may make it difficult in the management of specific conditions, then the presence of the butterfly helps in critical condition

Strategies for opening valves are determined by the operating condition of the engine. Especially at low rpm with little throttle valves are opened late and closed early to get a low and then raised a small scale.

When you ask the engine torque from low rpm, is reached in principle, but lifted the closure of the valve is anticipated. This enables you to reduce the junction with the valve, improving the air charge at low revs.

In the intermediate zone of operation, the system can perform double openings (multi-lift) create greater turbulence promoting the mixing of air and gasoline to achieve better combustion

One of the strengths of the MULTIAIR® is in the implementation, the system consists of a sovratestata that arises in the area where normally there is the axis of the cam the intake valve, as seen in cross section of the engine. On the rear cam cams are added to the MULTIAIR®.

Ultimately, the system has reduced dimensions and an engine is changed from classical to a MULTIAIR® simply replacing the camshaft with this classic above-head. In industrial terms this solution has considerable benefits.

The revolution that will bring the MULTIAIR® has been compared by Fiat to the Common Rail, another solution "Made in Italy" and then sold to Bosch. The comparison is no field in air: work with the diesel charge air mass and regulate only the amount of fuel. To obtain a similar flexibility on gasoline was necessary to enable a system to adjust both the air that the gas fed into the engine

An interesting aspect is the possibility of applying the Multia to diesel engines. The idea is to manage at least part of the air blown into the cylinders by reducing the formation of oxides of nitrogen, a necessary condition in order to come into Euro VI regulations.

Fiat, however, at least in the short term, will not sell the patent to a third party as happened to the Common Rail. But the car will use exclusively on its own group or at most it will sell a license to use "to its partners.