‘New’ Chrysler will Benefit from Fiat MultiAir Technology

A major part of the global strategic alliance between Chrysler and Fiat will be the ‘new’ Chrysler’s access to Fiat’s technology. One example is Fiat’s recently announced MultiAir electro-hydraulic, variable valve actuation technology. Developed by Fiat Powertrain Technologies, MultiAir will make its debut on the Alfa MiTo later in 2009. It will be used on a family of 16-valve, 1.4-liter naturally aspirated and turbocharged engines in 105, 135 and 170 horsepower versions. The MiTo will also have a Start&Stop feature that will temporarily shut off the engine while systems for the passengers' comfort still operate.

In spark ignition engines, the quantity and characteristics of the fresh air charge entering the cylinders is a key factor in controlling combustion, and thus performance, emissions, and fuel consumption. Traditionally, the air mass trapped in the combustion chamber is controlled by keeping the intake valve opening constant and adjusting upstream pressure through a throttle valve. This wastes about 10 percent of the input energy because the air charge has to be pumped from a lower intake pressure to atmospheric exhaust pressure.

Fiat’s MultiAir system uses an electro-hydraulic valve actuation system based on the automaker’s experience gained with its common rail developments for diesel engines. MultiAir features direct air charge metering at the cylinder inlet ports using advanced electronic actuation and control of the intake valves, while maintaining a constant natural upstream pressure. The driver now controls valve actuation rather than the throttle.

While variable valve timing has been used by other automakers, Fiat’s MultiAir features electro-hydraulic actuation rather than electro-mechanical concepts. Fiat says its approach provides more flexibility in valve opening schedules and better dynamic response. MultiAir offers the flexibility of valve opening for air mass control on a cylinder-by-cylinder and stroke-by-stroke basis, a capability not usually available with electro-mechanical systems. Other benefits cited include its relative simplicity, low power requirements, intrinsic fail-safe nature, and potentially lower cost.

Reducing pumping losses brings a 10 percent reduction in fuel consumption and CO2 emissions. Using a power-orientated mechanical camshaft profile, MultiAir can increase maximum horsepower up to 10 percent. Low rpm torque is improved by up to 15 percent through early intake valve closing strategies that maximize the air mass trapped in the cylinders. Emissions of nitrogen oxides (NOx) can be reduced by up to 60 percent by internal exhaust gas recirculation (iEGR), with intake valves reopening during the exhaust stroke. Optimal valve control strategies during cold start and warm-up can bring up to a 40 percent reduction in unburned hydrocarbons (HC) and carbon monoxide (CO) emissions.

By using MultiAir with turbocharging, engines can be downsized so fuel economy can be increased by up to 25 percent without compromising performance. MultiAir is applicable to all internal combustion engines regardless of the fuel used. It will next be used as an integral part of a new two-cylinder engine family.

While initially developed for spark ignition engines burning light fuel ranging from gasoline to natural gas and hydrogen, MultiAir can also be adapted for diesel engines. Here, further reductions come from more efficient management and regeneration of the diesel particulate filter and NOx storage catalyst, thanks to the highly dynamic air mass flow control during transient engine operation.

MultiAir is just one example of the growth potential still available for the internal combustion engine that can be exploited using advances in engine management technologies. These techniques can be used to meet increasingly more stringent demands for improved fuel economy and reduced emissions without compromising performance, and indeed often enhancing performance along the way.