Fiat showed off the detail of its new MultiAir engines at the 2009 Geneva motor show – and we’ll finally be able to buy the tech on the new Alfa Romeo Mito supermini later in 2009. The brains behind the common-rail injection system that shook up diesel technology have now produced a new technology designed to make petrol engines more efficient and cleaner.
Engineers claim the MultiAir engines – which use electrohydraulic actuation, rather than the more widely available electromechanical systems – boost power and torque, while cutting CO2 by between 10% and 25% and other pollutants by up to 60%. The secret? Using electronic actuation and control of the intake valves to make the passage of air into and out of the cylinders more efficient.
Fiat MultiAir: the new technology
Fiat’s new system uses intake valves operated by a conventional valve spring – but, crucially, they can be overridden by the MultiAir pack. A piston is attached to each intake valve through an hydraulic chamber; the chamber is controlled by an on/off solenoid valve – determining whether intake is governed by the conventional camshaft or the electronics.
Under maximum power, the solenoid valve is shut and the engine runs off the mechanical camshaft, which is calibrated for a long opening time and extra power. But MultiAir can then tweak intake performance on each cylinder for low-revs torque or part-load conditions.
Fiat claims its system is more flexible than the electromechanical variable valve lift systems used by companies such as Honda and BMW, which struggle to offer individual cylinder control, it claims.
MultiAir: when can I buy it?
The new valvework will appear this autumn on the Mito, on a new family of 16-valve 1.4-litre naturally aspirated and turbocharged engines. Next up is Fiat’s radical new two-cylinder engine family under development for future group small cars.
The next generation of MultiAir engines will be mated to direct injection and Fiat claims the tech can be rolled out to alternative-fuel engines too, including those powered by natural gas, hydrogen and biofuels.
>> Click ‘Next’ for Fiat’s full explanation of how MultiAir works
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We’d be the first to admit that MultiAir tech is rather complicated. So allow us to reproduce Fiat’s full explanation of MultiAir from their press material:
Fiat MultiAir technology: how it works
The operating principle of the system, applied to intake valves, is the following: a piston, moved by a mechanical intake camshaft, is connected to the intake valve through a hydraulic chamber, which is controlled by a normally open on/off solenoid valve.
When the solenoid valve is closed, the oil in the hydraulic chamber behaves like a solid body and transmits to the intake valves the lift schedule imposed by the mechanical intake camshaft.
When the solenoid valve is open, the hydraulic chamber and the intake valves are de-coupled; the intake valves do not follow the intake camshaft anymore and close under the valve spring action.
The final part of the valve closing stroke is controlled by a dedicated hydraulic brake, to ensure a soft and regular landing phase in any engine operating conditions.
Through solenoid valve opening and closing time control, a wide range of optimum intake valve opening schedules can be easily obtained.
For maximum power, the solenoid valve is always closed and full valve opening is achieved following completely the mechanical camshaft, which is specifically designed to maximise power at high engine speed (long opening time).
For low-rpm torque, the solenoid valve is opened near the end of the camshaft profile, leading to early intake valve closing. This eliminates unwanted backflow into the manifold and maximises the air mass trapped in the cylinders.
In engine part-load, the solenoid valve is opened earlier, causing partial valve openings to control the trapped air mass as a function of the required torque.
Alternatively the intake valves can be partially opened by closing the solenoid valve once the mechanical camshaft action has already started. In this case the air stream into the cylinder is faster and results in higher in-cylinder turbulence.
The last two actuation modes can be combined in the same intake stroke, generating a so-called Multilift mode that enhances turbulence and combustion rate at very low loads.