Fiat's Multiair Engine

January 29, 2010
The truly cool thing about internal combustion engines is there's always another creative way to skin the power/efficiency/emissions cat. Fiat's Multiair technology is a prime example. Even though variable valve timing (VVT) was first used here thirty years ago (by Alfa Romeo), Fiat engineers invented a clever twist on the idea which is already in production for Europe and will surely be used future Chrysler engines.
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The standard VVT approach is to use electronic controls to adjust the mechanical actuation between the engine's cam lobes and the valve stems. Altering both the timing and sometimes the lift of the valves can increase the power produced while diminishing both emissions and fuel consumption.
Multiair changes an important piece of the puzzle. In place of the adjustable mechanical link between cam and valve, Multiair imposes a small hydraulic connection to convey the forces that open the valve. An electronic solenoid valve plumbed into this hydraulic cam-to-valve connection quickly alters valve opening and lift in response to commands from the engine computer. So far Multiair works only on the intake valves.
What Multiair achieves that's not possible with alternative VVT approaches is cylinder-to-cylinder and cycle-to-cycle adjustability. It's so quick on its feet that two distinct intake valve opening events can be achieved in the same combustion cycle. That, according to Fiat, is handy for inducing turbulence (swirl and or tumble) in the combustion chamber, promoting quick flame travel and more complete burning of the fuel-air charge.
High-lift, long-duration intake cam lobes provide maximum power throughout the rpm range. Multiair essentially plays dead under these conditions to allow maximum intake valve lift and (open) duration. But when Multiair is programmed to lift the intake valve less than the full amount and to close it earlier than normal, torque is improved in the lower half of the rpm range.
During cruising, intake valve lift is lessened so that the throttle can be opened wide to greatly diminish pumping losses. With Multiair, it's possible to coordinate intake valve lift and timing throughout the entire rpm band and at all load settings to provide optimum performance.
Fiat claims a 10-percent gain in peak power, 15-percent more torque, and 10-percent better fuel economy. Combining Multiair with turbocharging and reduced displacement raises the efficiency benefit to 25-percent. There may also be cost benefits over conventional VVT since the hardware required here is quite modest in scope. One possible drawback is the congestion that results at the top of the cylinder head. This may be why Fiat has not yet combined Multiair with direct fuel injection.
In the 1960s, Fiat was the first car maker to patent a variable valve timing system that used engine oil pressure to adjust the fulcrum location for the cam followers, thereby facilitating variable timing and lift. In the 1980s, Fiat engineers (and many others) began studying the practically of camless engines -- with valves operated directly by electromagnets (solenoids). What they found was this approach consumed excessive electrical energy and offered no easy fail-safe. But witnessing strides made with common rail diesel fuel injection in the 1990s, Fiat persevered to keep gasoline engines in the game. Their Multiair has to be considered the better mousetrap in the VVT category.
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Broader applications for this technology are not difficult to imagine. What if Multiair could be applied to the world's most popular pushrod V-8s, such as those powering various GM pickups, SUVs, and a couple of Chevrolet sport hounds (Corvette, Camaro)? In place of today's two-valve cylinder heads, you'd have revised designs with four valves per cylinder and hydraulic actuation. As in the Fiat application, the solenoid control valves would provide the desired variable timing and lift. It could be done.
The pity is that GM and Fiat dissolved their technological exchange partnership a few years ago (at great cost to GM). But the good news is that a Multiair engine will soon be manufactured in Dundee, Michigan, by Chrysler for use in the Fiat 500 expected to go on sale late next year. After buying out partners Hyundai and Mitsubishi and investing $179-million in tooling, this wholly-Chrysler-owned facility is primed and ready to manufacture state-of-the art 1.4-liter 4-cylinder engines.
In Europe, Fiat's Punto and Alfa-Romeo's MiTo are already powered by Multiair Fire (fully integrated robotized engine) designs. Two versions are offered -- a 105-hp normally aspirated edition and a 135-hp turbo. The coming Alfa-Romeo Giulietta will also be powered by a Multiair engine.
Like direct injection, HCCI, wide-ranging electronic controls, and cylinder shut down, Multiair is just the latest good idea that gives the internal combustion engine a stay of execution until something dramatically superior comes along.


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