MultiAir is the new electro-hydraulic system of engine valves for dynamic and direct control of air and combustion, cylinder by cylinder and stroke by stroke. The key parameter to control gasoline engine combustion, and therefore performance, emissions and fuel consumption, is the quantity and characteristics of the fresh air charge in the cylinders. In conventional gasoline engines the air mass trapped in the cylinders is controlled by keeping the intake valves opening constant and adjusting upstream pressure through a throttle valve. One of the drawbacks of this simple conventional mechanical control is that the engine wastes about 10% of the input energy in pumping the air charge from a lower intake pressure to the atmospheric exhaust pressure. A fundamental breakthrough in air mass control, and therefore in gasoline engine technology, is based on direct air charge metering at the cylinder inlet ports by means of an advanced electronic actuation and control of the intake valves, while maintaining a constant natural upstream pressure. In the mid 90’s Fiat Group research efforts switched to electro-hydraulic actuation, leveraging on the know-how gained during the Common Rail development. The goal was to reach the desired flexibility of valve opening schedule air mass control on a cylinder-by-cylinder and stroke-by-stroke basis. The electro-hydraulic variable valve actuation technology developed by Fiat was selected for its relative simplicity, low power requirements, intrinsic fail safe nature and low cost potential.
MultiAir is a versatile technology, easily applicable to all gasoline engines and with future potential developments also for Diesel engines.
The MultiAir technology ensures air control in spark ignition engines without using the throttle valve and with a high level of flexibility if compared to conventional mechanical valve train systems. This electro-hydraulic valve actuation technology is based on the interposition, between cam and intake engine valve, of an oil volume (high pressure chamber) that can be adjusted through the utilization of an on-off solenoid valve, controlled by a dedicated electronic control unit.
There is no limit to adjusting the valve lift profile to meet engine air needs, at every running stage and without penalizing fuel consumption. Different strategies (Early Intake Valve Closing – EIVC, Late Intake Valve Opening – LIVO or Multi-Lift) can be used to optimize combustion efficiency, with notable benefits in terms of power, torque, consumption and emissions. The potential of this electronic valve control system is thus fully utilized through the MultiAir engine control system. Moreover, air pressure upstream the valves, always constant, and the high actuation dynamic of the system (from partial load to full load in one engine cycle) allows for an increasing and prompt engine torque response, both for aspirated and turbo engines, enhancing the so called Fun-to-Drive. The MultiAir technology has been conceived to meet future engine requirements and to become perfectly integrated with other technologies more and more applied on gasoline engine, like turbo-charging and fuel direct injection. Synergy of these technologies will lead to higher performance gasoline engines in the future, with further reduced consumption and compliance with future EURO 5 emission limits. MultiAir is also applicable to Diesel engines with significant reduction of NOx emissions (in line with EURO6) assuring at the same time high performance and drivability as well as further reduced consumption.
Load control without throttle valve, Lower consumption
Excellent volumetric efficiency, Performance / Fun to drive
Direct and fast valve control, Fun to drive
Optimised combustion control, Lower consumption / emission
Thanks to a direct control of the air through the intake engine valves without using the throttle, Multiair helps reducing fuel consumption; pollutant emissions are likewise reduced hrough combustion control. The MultiAir Technology potential benefits for gasoline engines can be summarized as follows: Maximum Power is increased by up to 10% thanks to the adoption of a power-oriented mechanical cam profile. Low-rpm Torque is improved by up to 15% through early intake valve closing strategies that maximize the air mass trapped in the cylinders. Elimination of pumping losses brings a 10% reduction of Fuel Consumption and CO2 emissions, both in Naturally Aspirated and Turbo charged engines with the same displacement. MultiAir Turbocharged and downsized engines can achieve up to 25% Fuel Economy improvement over conventional . Naturally Aspirated engines with the same level of performance. Optimum valve control strategies during engine warm-up and internal Exhaust Gas Recirculation, realized by reopening the intake valves during the exhaust stroke, result in emissions reduction ranging from 40% for HC / CO to 60% for NOx .
Constant upstream air pressure, atmospheric for Naturally Aspirated and higher for Turbocharged engines, together with the extremely fast air mass control, cylinder-by-cylinder and stroke-by-stroke, result in a superior dynamic engine response
MultiAir, initially developed for Spark Ignition engines burning light fuel ranging from gasoline to Natural Gas and hydrogen, has wide potential also for Diesel engine emissions reduction. Intrinsic NOx reduction of up to 60% can be obtained by internal Exhaust Gas Recirculation (iEGR) realized with intake valves reopening during the exhaust stroke, while optimal valve control strategies during cold start and warm-up bring up to 40% HC and CO reduction of emissions.
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