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Fiat’s more efficient form of combustion

The general design of the internal combustion engine, hasn’t really changed all that much since the 1800s. But new technologies are helping to improve its performance, such as the Fiat 500’s MultiAir system.

The general design of the internal combustion engine, which burns gasoline to create a rotational force to turn the vehicle’s wheels, hasn’t really changed all that much since the 1800s.

But new technologies are helping to improve its performance, such as the Fiat 500’s MultiAir system.

Gasoline gets into an engine and exhaust escapes through precisely-timed intake and exhaust valves.

In most engines, these valves are operated by the lobes on a spinning camshaft.

While the MultiAir engine uses a camshaft for the exhaust valves, the intake valves are activated instead by pressurized engine oil controlled by electronic solenoids.

“We’ve removed the direct mechanical linkage to the valve,” says Mike Vincent, platform manager for the 1.4-litre MultiAir engine. “The advantage is all about trapping the most amount of air and fuel you can deliver on a given cycle, making the combustion more efficient.”

While the system is more expensive than a camshaft, Vincent says that in an otherwise equal comparison of engine and vehicle size, the MultiAir system reduces both fuel consumption and emissions by up to 10 per cent each. As well, since it provides better low-end power, the small engine feels very peppy and the car is fun to drive.

A major advantage to MultiAir is that it continually and precisely controls how far the valve lifts up each time it opens.

“A mechanical camshaft opens the valve to the same degree each time, and it must be optimized for full throttle,” Vincent says. “You have maximum lift on wide-open throttle, but at low speeds, such as idling or in city traffic, you don’t need all the lift that’s available, and you’re wasting the opportunity to keep air in the cylinder. With MultiAir, the amount of oil pressure controls how much the valve opens.”

The system can change the amount of lift very rapidly, even starting the sequence normally and then closing the valve early if it’s required.

A camshaft is still used on the exhaust valves mostly due to design, Vincent says.

“The packaging becomes very difficult to manage if you add the hardware on both intake and exhaust. The goal is to maximize the amount of fresh air trapped, so control on the intake side was the highest priority.”

 
 
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